Expanded Leaf Stage Research Articles

Detrimental impacts of concomitant application of cadmium and pesticides are ameliorated by 24-epibrassinolide through alteration in oxidative status and CYP genes expression in Zea mays L.

The ameliorative impact of 24-epibrassinolide (EBL) was assessed under toxicity of cadmium (Cd) and three different pesticides including diazinon (DZ), imidacloprid (IMI), and chlorpyrifos (CPS) in maize plants. Maize seeds were pre-treated with 0.01 μM of EBL and grown in soil contaminated with 100 μM Cd for one month. Then, at five fully expanded leaf stage, plants received DZ, IMI, and CPS pesticides separately by foliar spray and were harvested five days later. The EBL seed primed plants, grown in soil contaminated with Cd and exposed to pesticides, exhibited higher deleterious photosynthesis (Pn) and stomatal conductivity (Gs) compared to un-EBL-treated plants. A considerable decrease was observed in the pesticide's residue and Cd, MDA and H2O2 contents of EBL + Cd + Pesticide treated plants compared to the Cd + Pesticide groups plants. Higher phenol, flavonoid and protein contents, as well as increment in SOD, CAT, POD, APX, PAL, GST, and GR enzymes activity were detected in EBL + Cd + Pesticide groups compared to the plants imposed with Cd + Pesticides. The expression analyses of four CYP family members including CYP71C1, CYP71C3v2, CYP72A5, and CYP81A9 revealed downregulation under Cd and Cd + pesticides treatments, while EBL seed priming highly induced transcript abundance of CYP71C1 (EBL + Cd + IMI); CYP71C3v2 (EBL + Cd + DZ & EBL + Cd + IMI) and CYP81A9 (EBL + Cd + DZ & EBL + Cd + CPS), specifically. The higher mRNA accumulation of CYP72A5 gene was exhibited under all three different EBL + Cd + pesticides treatments. The 24-epibrassinolide alleviates the adverse impacts of Cd and pesticides via the activation of enzymatic and non-enzymatic components to eliminate ROS through the up-regulation of CYP genes. This facilitates conjugation of glutathione to pesticides residue, leading to their rapid transportation into the vacuole or out of the membrane.

Soil and leaf phosphorus thresholds for modern potato production systems in tropical Oxisols

Precise diagnosis and prognosis of phosphorus (P) nutrition are essentials to improve P use efficiency and sustainability in potato cropping systems. Here, variable potato crop responses of 13 field experiments (2011–2022) were assessed to determine critical soil P-resin (SPresin) and potato leaf P (LP) concentrations to achieve maximum tuber yield in tropical Oxisols. The study comprised four experiments with the factorial design of potato cultivars in response to P fertilization rates and nine experiments with P fertilization rates as fixed effects. Relationships between initial SPresin test, LP measured at the third or fourth expanded leaf stage (i.e., 29–37 days after emergence, DAE), and relative total fresh tuber yield (RY) (yield of control/yield at highest P rate) were analyzed using linear-plateau, Mitscherlich, and quadratic-plateau regression models. A wide range of total fresh tuber yield (3.2–59 Mg ha-1) and LP (1.3–5.7 g P kg-1) were observed across experiments. The LP values in control plots was positively related with initial SPresin, reaching a maximum LP of 3.8 g P kg-1 at an initial SPresin of 80 mg P dm-3 (averaged across models). The relationship between RY and initial SPresin was significant in the three regression models (p < 0.05; R2 = 0.71–0.74). Maximum tuber yield was reached with the SPresin value of 93 mg P dm-3 (averaged across models). Across experiments and P fertilization rates, relationships between RY and LP were significantly described in the three regression models (p < 0.05; R2 = 0.55–0.67). The critical LP of 4.5 g P kg-1, obtained from the average across models, is proposed as the optimum indicator of potato P nutritional status to achieve maximum tuber yields in tropical Oxisols. These are the first critical P thresholds on a soil and environmental-specific conditions base available for tropical conditions in Brazil, timely informative in terms of optimization of P management to maximize tuber yield and P use efficiency, and minimize the risk of environmental P contamination.

The Application of Machine Learning Models Based on Leaf Spectral Reflectance for Estimating the Nitrogen Nutrient Index in Maize

Non-destructive acquisition and accurate real-time assessment of nitrogen (N) nutritional status are crucial for nitrogen management and yield prediction in maize production. The objective of this study was to develop a method for estimating the nitrogen nutrient index (NNI) of maize using in situ leaf spectroscopy. Field trials with six nitrogen fertilizer levels (0, 75, 150, 225, 300, and 375 kg N ha−1) were performed using eight summer maize cultivars. The leaf reflectance spectrum was acquired at different growth stages, with simultaneous measurements of leaf nitrogen content (LNC) and leaf dry matter (LDW). The competitive adaptive reweighted sampling (CARS) algorithm was used to screen the raw spectrum’s effective bands related to the NNI during the maize critical growth period (from the 12th fully expanded leaf stage to the milk ripening stage). Three machine learning methods—partial least squares (PLS), artificial neural networks (ANN), and support vector machines (SVM)—were used to validate the NNI estimation model. These methods indicated that the NNI first increased and then decreased (from the 12th fully expanded leaf stage to the milk ripening stage) and was positively correlated with nitrogen application. The results showed that combining effective bands and PLS (CARS-PLS) achieved the best model for NNI estimation, which yielded the highest coefficient of determination (R2val), 0.925, and the lowest root mean square error (RMSEval), 0.068, followed by the CARS-SVM model (R2val, 0.895; RMSEval, 0.081), and the CARS-ANN model (R2val, 0.814; RMSEval, 0.108), which performed the worst. The CARS-PLS model was used to successfully predict the variation in the NNI among cultivars and different growth stages. The estimated R2 of eight cultivars by the NNI was between 0.86 and 0.97; the estimated R2 of the NNI at different growth stages was between 0.92 and 0.94. The overall results indicated that the CARS-PLS allows for rapid, accurate, and non-destructive estimation of the NNI during maize growth, providing an efficient tool for accurately monitoring nitrogen nutrition.

Developmental and phytochemical changes in pot marigold (Calendula officinalis L.) using exogenous application of polyamines

Polyamines (PAs) are natural active compounds having more than two amino groups that play important roles in many physiological and developmental processes in plants. The purpose of this research was to see how foliar polyamine spray affected growth and photosynthetic indices, as well as secondary metabolites and antioxidant activity of the aqueous and methanolic extracts of pot marigold (Calendula officinalis L.). The experiment lasted for three months and was arranged in a randomized complete design with four replications. Three separate concentrations (0.5, 1 and 2.5 mM) of spermine (SPM), spermidine (SPD), and putrescine (PUT) were sprayed at four/five fully expanded leaf stage and some physiochemical attributes were evaluated. The treatments caused a significant increase in morphological and photosynthetic parameters and total oil. There were also significant variations in total phenolic and flavonoid content. Compared to other polyamines, 1 mM SPD foliar spraying showed the greatest effect. Furthermore, the highest antioxidant capacity (DPPH* scavenging assay, ferric reducing antioxidant power (FRAP), Trolox equivalent antioxidant capacity (TEAC) and β-carotene bleaching activity) was observed in the 1 mM SPD treatment. The results showed that the calendula essential oils (EOs) were rich in sesquiterpenes hydrocarbons (55.92–95.94%), with c-Cadinene and d-Cadinene as the major sesquiterpenes in the EOs. Also, the flowers were rich sources of carotenoids (lutein, flavoxanthin and luteoxanthin) following polyamines application. Hence, it can be inferred that polyamines specially spermidine would find a wide range of application in pharmaceutical industries due to its impact on antioxidant properties of phenolic and flavonoid compounds.

First report of Ethiopian tobacco bushy top virus and its associated satellite RNA infecting common bean (Phaseolus vulgaris L.) in Zambia.

During surveys for common bean viruses in Central Province of Zambia in April 2018, symptoms of bushy top, deep green curled branches and patchy leaf chlorosis were observed on five plants in a 2-ha farmer's field. Total RNA was isolated from symptomatic leaf samples using the CTAB method (Chang et al. 1993). The RNA from one sample (CP414-1) was used to construct a cDNA library with the Illumina TruSeq RNA Library Prep Kit (Illumina, San Diego, CA), followed by high-throughput sequencing (HTS) on the Illumina MiSeq platform that generated ~3.1M single-end raw reads of ~300 nucleotides (nt) each. A total of 355,885 reads showed hits to Ethiopian tobacco bushy top virus (ETBTV; Umbravirus), ETBTV satellite RNA (satRNA) and peanut mottle virus (PeMoV, Potyvirus) based on BLASTn analysis. The full-length genomes of ETBTV (4239-nt; MT225089), its satRNA (521-nt; MT225092) and PeMoV (9,643-nt) were assembled from the HTS reads using Geneious R11.1.2 (Biomatters, Auckland, New Zealand). The obtained complete genome sequences of ETBTV (MT225089) and ETBTV satRNA (MT225092) shared 88% and 95% nt identities, respectively with the corresponding viral (KJ918748) and satRNA (KJ918747) sequences of isolate 18-2 (Abraham et al. 2014). The near complete PeMoV genome was 89% identical to isolate Liaoning (MH270528). The HTS results were validated by two-step RT-PCR analyses of the five field-collected samples using newly designed primer pairs (data not shown). All five samples gave the expected 988-bp ETBTV-specific and 521-bp satRNA-specific DNA bands while three samples produced the expected 2100-bp PeMoV-specific fragment. The virus specificities of the agent specific PCR fragments were ascertained by Sanger sequencing (ETBTV: MT225090-91; ETBTV satRNA: MT225093-94; PeMoV: MT900843-44) and they shared 98-100% identities with their corresponding HTS-derived sequences. To further probe for the presence of an ETBTV helper virus, the samples were screened by RT-PCR with the degenerate primer pair Lu1-mod-F/C2R3 that was modified from Robertson et al. (1991). The expected 245-bp DNA bands was obtained from all five samples, indicating the presence of a possible luteovirus or polerovirus target in these samples. The BLASTn analyses of the two Sanger sequenced gel-eluted products (MT900845-46) showed that they shared 100% identity with each other and 96% nt identity with cowpea polerovirus 1 (CPPV1, KX599163). Leaf tissue extracts from a common bean plant that was confirmed by RT-PCR to be positive for all four agents were rub-inoculated onto Nicotiana occidentalis and common bean (Sutter Pink) plants (n=5 each) at the three fully expanded leaf stage, with a buffer inoculation as control. Systemic foliar symptoms consisting of leaf deformation, stunting and leaf bushy top were observed on all ten plants, 10 days post-inoculation whereas the control plants remained symptomless. All the test plants were screened by RT-PCR as described above. The results showed that all five N. occidentalis plants were positive for ETBTV+ETBTVsatRNA, the five common bean plants tested positive for ETBTV+satRNA+PeMoV, and all 10 plants of both species were negative for CPPV1. To the best of our knowledge, this is the first report of ETBTV, ETBTV satRNA and CPPV1 infecting common bean in Zambia, and the first molecular based confirmation of PeMoV occurrence in the country. Ongoing studies are focused on determining the extent of the disease spread and assessment of its economic impact.

Fuzzy logic simulation of oat yield after using hydrogel and nitrogen biopolymer management

The fuzzy logic is an efficient tool for simulation and validation of new technologies in agriculture. The objective of the study is to adapt the fuzzy logic model for simulation of biomass and oat grain yield by nitrogen involving the nonlinearity of the maximum air temperature in the conditions of use of the biopolymer hydrogel, considering high succession systems and low release of residual N. The study was conducted in 2014 and 2015, in a randomized block design with four replicates in a 5 x 5 factorial. Five hydrogel doses (0, 30, 60, 90 and 120 kg ha-1) were added in the groove next to the seed; and 5 doses of N-fertilizer (0, 30, 60, 90 and 120 kg ha-1) applied at the fourth expanded leaf stage, respectively. The cultivar was URS Corona. The pertinence functions and the linguistic values established in the input and output variables to simulate the biomass yield and oat grains in the succession systems are adequate observed productivity. The fuzzy model makes it possible to estimate the biomass and oat grains productivity efficiently under the conditions of use of the hydrogel as a function of the nitrogen doses and maximum air temperature, adding to the existing models of simulation.

Timing and Splitting of Nitrogen Side-Dress Fertilization of Early Corn Hybrids for High Grain Yield

ABSTRACT Currently, most nitrogen fertilizer is side-dressed when corn is in the four (V4) to eight (V8) expanded leaf stage. However, recent studies have shown that modern hybrids take up high amounts of nitrogen during grain filling. This indicates that a late nitrogen fertilization, at the time of crop flowering, may be important to optimize corn agronomic performance. This study aimed to evaluate the effect of the timing and splitting of nitrogen side-dress application on the agronomic performance of early [...]

Comparative Leaf Phenology of White Oak and Northern Red Oak

In the landscape, loss of interveinal tissue in developing leaves (leaf tatters) is common for white oak (Quercus alba L.), but not northern red oak (Quercus rubra L.). Previous research identified the cause of leaf tatters, as exposure of unfolding leaves, to low concentrations of chloroacetanilide herbicides. Both white oak and northern red oak were injured by these herbicides at the leaf unfolding stage. Reports from landowners suggest white oak is injured more often than red oak, leading us to theorize that white and northern red oak leaves emerge at different times, and white oaks were more likely to be at the leaf unfolding stage when chloroacetanilide herbicides are applied. A study of comparative leaf phenology of white and northern red oak was done at three sites in Urbana, IL. Identifying oak pairs was challenging, and at each location, four to six paired mature white oak and northern red oak trees were used to observe phenological events. Key development stages (swollen bud, leaf unfolding, or fully expanded leaf stages) were considered to have occurred when reached by greater than 50% of the canopy. Northern red oak expanded leaf stage occurred earlier when compared to white oak. Time between phenological events was similar for both species. Although northern red oak leaves emerged earlier, there was a range of emergence times within short distances. Difference between locations illustrates the problem in predicting tree phenology even among populations a few kilometers apart. Leaf phenology alone does not explain leaf tatters, and other factors including distribution differences in oak species must explain landowner observations of tree injury. There was a strong correlation between growth phases of the two oak species with cumulative growing degree days, cumulative rainfall, and day length.

Comparative proteomic analysis of leaves between photoperiod-sensitive and photoperiod-insensitive maize inbred seedlings under long day treatments

Day length is an important environmental factor affecting the growth and development of maize (Zea mays), a short day (SD) plant grown in different latitudes. Leaf has been recognized as the light perceiving and signal producing organ. Under long day (LD) conditions, photoperiod-sensitive induction phase in maize begins at the fourth fully expanded leaf stage. However, the changes of maize leaf proteome in response to LD are largely unknown. To reveal maize proteome response to LD, proteins extracted from newly expanded fifth, sixth and seventh leaves from maize inbred line 496-10 (photoperiod sensitive) and Huangzao4 (HZ4, photoperiod insensitive) under LD treatments were compared via gel-based proteomic approach. As a result, eleven differentially expressed proteins were identified between 496-10 and HZ4 by mass spectrometry. This difference in protein accumulation was highly reproducible during the fifth to seventh leaf stages and most obvious at the seventh leaf stage. The identified proteins are mainly involved in circadian clock or iron metabolism, light harvesting and photosynthesis, nucleic acid metabolism and carbon fixation or energy metabolism. This study provides new insight into the influences of LD treatment on SD plants, such as maize, at proteome level.

English

Zea mays crop has been standing out in the Brazilian Cerrado of Piau&iacute; State, located in the Northeastern Brazil. However, despite the high technology level utilized, yield levels are still below the expectation, mainly due to the mismanagement of nitrogen (N). This experiment was conducted in field using single-cross hybrid 30F53 from Pioneer&reg;. The experiment was conducted as completely randomized blocks design with nine treatments and four replications. The treatments consisted of five rates of N as urea, equivalent to 0, 60, 120, 180 and 240 kg N ha-1. It was applied twenty kg N ha-1 at sowing and the rest as topdressing. The splits comprised the application of 50% at the four expanded leaf stage (V1) + 50% at the eight expanded leaf stage (V2) or total rates at four expanded leaf stage. Leaf N content, leaf relative chlorophyll content, plant height, ear height, stem diameter, yield, grains per ear and rows per ear, grains per row, 1000 grains weight and agronomic efficiency index were measured. Nitrogen significantly increased agronomic characteristics of corn and the highest grain yield was obtained with 190.65 kg ha-1 N. Plant height, relative chlorophyll content, leaf N content, plant biomass, stem diameter, thousand seed weight, yield and agronomic efficiency index were positively influenced by the rates of nitrogen. The split of topdressing in twice was not suitable in the dystrophic Yellow Latosol of the Piau&iacute; Cerrado. Plant height, relative chlorophyll content, ear insertion height, stem diameter, grains per ear and rows per ear, grains per row and agronomic efficiency index positively correlated with grain yield. &nbsp; Key words: Agronomic efficiency index, yield, relative chlorophyll content.

First Report of Bacterial Wilt Caused by Erwinia tracheiphila on Pumpkin and Watermelon in New Mexico.

Pumpkin (Cucurbita pepo L., cv. Magic Lantern) and watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai, cvs. Millionaire and Sangrea) plants with wilting leaves and collapse of entire vines were observed during the 2005 and 2006 growing seasons in several fields in southwestern New Mexico (Luna and Hidalgo counties) with an incidence ranging from 7 to 25% and less than 1% in pumpkin and watermelon fields, respectively. Sticky, hyaline strands were visible when vines were cut transversally, indicative of bacterial wilt caused by Erwinia tracheiphila (2). In the pumpkin fields, 12-spotted cucumber beetles, vector insects of E. tracheiphila, were found on plants at the first-true-leaf stage, which were treated with dimethoate. At the 4- to 5-leaf stage, 5 to 10% of the plants were wilted and were removed by hand. Less than 1% of the plants showed symptoms prior to bloom, when a high population of beetles was observed, and the fields were treated with thiamethoxam. To isolate the causal agent of the wilt symptoms, six, 1-cm vine segments and three to five beetles were surface sterilized in 1% NaOCl for 2 min, rinsed and macerated in sterile distilled water, and plated onto potato dextrose agar, nutrient agar, and King's medium B. After incubation at 25°C, bacterial colonies emerged on all media and were grayish white-to-cream, circular, smooth, and glittering. Isolated bacteria were gram negative, did not grow at 39°C, produced hydrogen sulfide gas from hydrolysis of cysteine, and did not hydrolyze litmus milk and starch. With Ready-To-Go PCR beads and 16S rDNA-based primers ET1/ET2 (1), a 700-bp product was obtained from each of two isolates, consistent with previously reported data for E. tracheiphila (1,3). For the pathogenicity tests, 10 seedlings of pumpkin cv. Magic Lantern and watermelon cv. Millionaire were inoculated with each isolate in the greenhouse at the second fully expanded leaf stage using two methods. In the first method, stems were injected with bacterial suspension (106 CFU/ml) using a hypodermic needle. In the second method, a dab of bacterial colonies was taken with a sterile toothpick to stab the cotyledonary axils. Control seedlings were stem injected with distilled water or stabbed with a sterile toothpick. The experiments were conducted four times. Inoculated plants were placed in a humid chamber at 23 to 25°C. Plant wilting was observed within 4 days when stab inoculated with toothpicks and within 7 to 10 days when stem injected with bacterial suspension. Bacterial colonies recovered from inoculated plants were identical to those recovered from field infected plants. To our knowledge, this is the first report of bacterial wilt on pumpkin and watermelon in New Mexico.

Morphological and Physiological Responses of Sorghum (Sorghum bicolor L. Moench) to Waterlogging

The aim of this study was to investigate the effect of waterlogging on morphological and physiological traits of sorghum (Sorghum bicolor L. Moench) cultivars. Four sorghum cultivars, cv. Wray, Keller, Bailey (sweet cultivar) and cv. SP1 (forage cultivar) at five expanded leaf stage were subjected to 20 days of waterlogging and drained pots were kept as the control. Twenty days of waterlogging did not cause a significant difference in shoot and root biomass among cultivars. Flooding reduced leaf area (69%), plant height (30%) and youngest leaf expansion rate of all cultivars but severely reduced in SP1 (35-80%). Flooding promoted leaf senescence of all cultivars and biomass allocation to shoot (increase in shoot/root) in Wray, Keller and Bailey, but increased biomass partitioning to root in SP1. The initiation of new nodal root was noted in SP1, whereas the ability to maintain root surface area by increase in longest root length and nodal root development near soil surface was found in Wray. Photosynthetic rate, stomatal conductance and transpiration rate were severely reduced under waterlogging conditions of sweet cultivars (65-78%), but enhanced over the control in forage cultivar (56%). The ability to conserve root surface area, allocate more biomass to shoot during waterlogging and develop root near soil surface may support new growth in Wray, whereas the ability to maintain leaf gas exchange parameters in SP1 was due to the active nodal root growth. Nevertheless, there was no relationship between photosynthetic rate and shoot growth of sorghum under anaerobic conditions.

Vernalization of Seed and Plantlets and Development of Globe Artichoke

Annual production of globe artichoke [Cynara cardunculus var. scolymus (L.) Fiori] requires vernalization of the plants, either through cold treatment of transplants or from natural temperature conditions in the spring. To evaluate cold treatment on productive traits in artichoke, two experiments were performed. In the first experiment, dry seeds, plantlets at the cotyledon stage, and plants with two expanded true leaves were subjected to 3°C for 10 days. In the second experiment, dry seeds, seeds soaked in water, and germinated seeds were subjected to 3°C for 10 days. Days to first harvest (FH), total yield (TY), number of buds (NB), and mean head weight (MW) were evaluated. Treatment did not affect FH, but treatment affected NB and TY in the first experiment. Plants developed from seedlings treated at the two-leaf stage had increased NB and TY. In the second experiment, vernalization decreased NB, bud weight, and TY below that of controls. Cold treatment of seedlings at the two expanded leaf stages may have the potential to enhance yield.

Injury on White Oak Seedlings from Herbicide Exposure Simulating Drift

Herbicide drift to landscape and woodland trees is a particular concern in midwestern United States where the topography is relatively flat, large-scale agriculture relies on herbicides, and housing developments and woodlands are intermingled with agricultural fields. Recently, leaf abnormalities (called leaf tatters) have been reported on white oak (Quercus alba L.). We evaluated the effects of field corn herbicides on white oak at the swollen bud, leaf unfolding, and expanded leaf stages. Container-grown white oak seedlings were treated with 1%, 10%, and 25% standard field use rates of 2,4-D isooctyl ester, glyphosate, 2,4-D isooctyl ester + glyphosate, dicamba, acetochlor + atrazine, and metolachlor. Loss of interveinal tissues (leaf tatters) occurred after treatment with the chloroacetanilide herbicides, acetochlor (+ atrazine) and metolachlor, only when oaks were in the leaf unfolding stage. No other herbicide caused tatter-like symptoms. Dicamba and 2,4-D ester applied at the leaf unfolding stage caused leaf cupping, downward rolling of leaf margins, elongation of leaf tips, leaf strapping with parallel veination, and initial leaf cupping followed by death of the growing point. Glyphosate applied at either the leaf unfolding or expanded leaf stage caused leaf chlorosis and necrosis, leaf tip browning, and curling of leaves. Herbicide applications near white oak should be timed before leaf unfolding or after the expanded leaf stages.

Seletividade de diferentes herbicidas à base de glyphosate a soja RR

Com o objetivo de avaliar a seletividade de variedades de soja transgênica (CD 214 RR e M-SOY 8008 RR) a diferentes herbicidas à base de glyphosate (Roundup Ready, Roundup Transorb, Roundup Original, Roundup WG, Polaris, Gliz, Glifosato Nortox e Trop), foi desenvolvido experimento em condições de campo, no ano agrícola 2005/2006, na Fazenda de Ensino, Pesquisa e Produção da UNESP, campus de Jaboticabal, SP. O delineamento experimental utilizado foi o de blocos ao acaso, num esquema de parcelas subdivididas, com quatro repetições. Os herbicidas foram aplicados na dose de 1,2 kg ha-1 de equivalente ácido de glyphosate, quando as plantas de soja se encontravam com a segunda folha trifoliolada totalmente expandida. Não foram observados sintomas de intoxicação dos herbicidas nas plantas de soja. Quanto às demais características avaliadas, a interação variedade x herbicida não foi significativa, indicando que os fatores comportaram-se de forma independente. Entre as variedades, as plantas de M-SOY 8008 RR apresentaram maior altura e número de nós, porém obtiveram menor produtividade de grãos que as de CD 214 RR, devido ao menor número de grãos por vagem. No tocante aos herbicidas, não houve diferença significativa entre eles, ou seja, eles não influenciaram o desenvolvimento vegetativo e reprodutivo das plantas de soja.

Occurrence of Phytophthora Blight on Pumpkin in New Mexico.

During 2004 and 2005, two fields in Luna County and one field in Doña Ana County in southern New Mexico displayed pumpkin (Cucurbita pepo cv. Magic Lantern) plants with necrotic spots on leaves and dark brown and water-soaked lesions on petioles, vines, and fruits. Lesions on several fruits were covered with white mycelial mats that were also visible in the lumen when fruits were sectioned. Areas of fields with plants displaying these symptoms ranged from 2 to 5%. Within affected areas, percentage of plants with symptoms ranged from 75 to 100%. Samples of leaves, vines, and fruits were collected for isolation of putative causal agents. In all instances, mycelial colonies emerged from leaf, vine, and fruit tissues placed on water agar and incubated at 23 to 25°C. Colonies were transferred to potato dextrose agar and V8 agar media for identification. Two mycelial isolates yielding cultures with white and stellate mycelium were recovered. Biometric data were collected on 50 sporangia produced using the mycelium-agar-disc-in-water method (1) under continuous fluorescent light for 7 days at room temperature. Sporangia were caducous, ellipsoid, and papillate with an average length of 42.6 μm and average breath of 25.6 μm. Sporangia had long pedicels with an average length of 71.5 μm. Oogonia that formed only when the isolates were paired with an opposing mating type tester of Phytophthora capsici had an average diameter of 29 μm with amphigynous antheridia. Both isolates were of mating type A1. These morphological features and biometric data are consistent with those reported for P. capsici (2). The two recovered isolates of P. capsici were tested in the greenhouse for pathogenicity on the pumpkin cv. Magic Lantern. In each of two trials, 25 plants at the first fully expanded leaf stage were inoculated by dispensing 5 ml of zoospore suspension (2,000 zoospores per ml) of each isolate on top of the soilless mix around the base of each plant. Within 5 to 7 days of inoculation, symptoms were visible as girdling, dark brown lesions on stems. Samples of stems from 10 infected pumpkin plants were plated on water agar. P. capsici was recovered from all sampled plants. Control plants (noninoculated) did not display any symptoms. Pumpkin isolates also were inoculated onto 30 chile pepper (Capsicum annuum) plants of cv. AZ-20, which is susceptible to P. capsici. In each of two trials, 15 chile pepper plants at the 6- to 8-leaf stage were inoculated by the same method used for pumpkin plants. Within 7 to 10 days, dark lesions appeared on stems followed by defoliation and wilting. P. capsici was recovered from sampled stem segments. Control plants (noninoculated) did not display any symptoms. Infection of pumpkin by P. capsici has been reported in several states in the United States such as Illinois, Michigan, and North Carolina (3). However, to our knowledge, this is the first report of P. capsici on pumpkin in New Mexico, and it has implications for chile pepper, a major crop in southern New Mexico known to be susceptible to P. capsici. The first occurrence of P. capsici on chile pepper was reported in 1922 (4). Pumpkin and chile pepper are grown in the same fields. In light of the cross-infectivity of P. capsici to both crops, it is not advisable for growers to continuously rotate pumpkin and chile pepper.

Growth and physiological responses of six barley genotypes to waterlogging and subsequent recovery

In this study, the growth response of 6 barley genotypes of different origin (3 from China, 2 from Australia, 1 from Japan) to waterlogging and subsequent recovery was evaluated in 2 different soil types, an artificial potting mix and a Vertosol. A range of physiological measurements was assessed, to develop a method to aid selection for waterlogging tolerance. Plants at the 3 or 4 expanded leaf stages were subjected to waterlogging for 3 weeks followed by 2 weeks of recovery. Both shoot and root growth was negatively affected by waterlogging. As waterlogging stress developed, chlorophyll content, CO2 assimilation rate, and maximal quantum efficiency of photosystem II (Fv/Fm) decreased significantly. The adverse effect of waterlogging was most severe for genotype Naso Nijo, intermediate for ZP, Gairdner, DYSYH, and Franklin, and least for TX9425 in both trials. Studies of the root anatomy suggested that such a contrasting behaviour may be partially due to a significant difference in the pattern of aerenchyma formation in barley roots. The adverse effects in stressed plants were alleviated after 2 weeks of drainage for all genotypes. In general, TX9425 continued to grow better than other varieties, whereas recovery of Naso Nijo was extremely slow. It is suggested that screening a small number of lines for waterlogging tolerance could be facilitated by selecting genotypes with least pronounced reduction of photosynthetic rate or total chlorophyll content, and for a larger number of lines, chlorophyll fluorescence is the most appropriate tool.

Inhibition of pre-penetration development of blast fungus during the infection of resistant rice cultivars

Spore germination and appressorium formation of the rice blast fungus, Magnaporthe grisea, were compared during infection of rice cultivars differing for their resistance to strain H5-3. On leaves of the susceptible cv. Sha-tiao-tsao neither spore germination nor appressorium formation were inhibited, in comparison to a control germination test in water on polystyrene. On the resistant cv. Tadukan, both spore germination and appressorium development were strongly inhibited whereas on the partially resistant cv. Shimokita a slight inhibition of germination and significant delay of appressorium formation was observed. Inhibitors of germination were not produced in leaf diffusates of the susceptible cultivar Sha-tiao-tsao. On the contrary, such compounds were excreted by leaves of the two resistant cultivars. The fungitoxicity of diffusate of cv. Tadukan was strong from 5 to 24 h after inoculation. The diffusate of cv. Shimokita was less toxic at 5 h but at 24 h it reached the same level of toxicity as diffusate of cv. Tadukan. Such antifungal plant metabolites accumulating in drops of inoculum may inhibit the pre-penetration development of the rice blast fungus and presumably contribute to disease resistance, including the partial resistance. Plant resistance to fungal diseases might be associated with the inhibition of pathogen development in host tissues during early stages of the infection. The rice blast fungus Magnaporthe grisea does not penetrate readily into leaves of some resistant rice cultivars (Heath et al., 1990; Koga and Kobayashi, 1982) or cannot spread over the first invaded cells (Arase et al., 1983; Peng et al., 1988; Kaur et al., 1984). Inhibition of spore germination and appressoria formation were observed during inoculation of leaf fragments from completely resistant rice cultivars (Lapikova and Dzhavakhiya, 1987). This may be due to plant defence responses (syntheses of lignin, phytoalexins and pathogenesis-related proteins etc.) which may liberate fungitoxic products into the extracellular space. Previously, we found that the partially resistant cultivar Shimokita in combination with strain H53 manifests a reduced infection frequency, smaller lesions and a reduced rate of spore production per lesion (Pasechnik et al., 1995), phenomena typical for partial resistance (Roumen et al., 1993). The prepenetration development of the rice blast fungus on such rice cultivars is not well documented. The aim of the present work was to assess whether fungal development is affected on the leaf surface of cv. Shimokita. The susceptible cv. Sha-tiao-tsao and the completely resistant cv.Tadukan were taken as controls and intact plants rather than leaf fragments were used for the assessment. We used strain H5-3 (race 007) of the rice blast fungus, Magnaporthe grisea (Herbert) Barr. The rice (Oryza sativa L.) cultivars differ in their resistance to race 007: the susceptible cv. Sha-tiao-tsao develops numerous lesions, on the completely resistant cv. Tadukan no visible symptoms are produced and cv. Shimokita exhibits partial resistance with the rare occurrence of compatible-type lesions. Plants were grown in a climatic chamber up to the fourth fully expanded leaf stage (Lapikova et al., 1994). The fourth leaf was used for the analyses. The central part of the leaf was fixed horizontally in an inoculation chamber (Lapikova et al., 1995) and a plastic ring (ID 3 mm, height 1 mm) was placed on the leaf. One drop (10 l)

Ovipositional Preference of Pear Psylla (Homoptera: Psyllidae) for Resistant and Susceptible Pear

Ovipositional preference of pear psylla, Cacopsylla pyricola Foerster, for selected Pyrus genotypes known to differ in nymphal feeding antixenosis was quantified in the field and greenhouse during the dormant-bud, green-tip, and fully expanded-leaf stages of bud phenology. Definite ovipositional preferences were displayed by pear psylla. Ovipositional antixenosis was particularly evident in Pyres communis L. and P. communis L. × P. ussuriensis Maxim. hybrids that were also known to have nymphal feeding antixenosis during the fully expanded-leaf stage. Although ovipositional and nymphal feeding antixenosis did show significant correlation, there were exceptions that suggest these two pear traits are independent. In greenhouse and field studies, we found that ovipositional antixenosis varied with bud phenology within pear genotypes, which indicated that ovipositional cues differed. However, several P. communis and P. communis × P. ussuriensis genotypes exhibited ovipositional antixenosis during all stages of bud phenology. Results of greenhouse ovipositional studies were similar to those observed for these pear genotypes in the field. Our greenhouse technique offers a rapid means of evaluating ovipositional antixenosis in pear genotypes compared with field studies, which are hampered by variable pear psylla populations, time, and space requirements.

Control of Fall Armyworm in Field Corn, 1985

Abstract 'Pool 24' corn was planted on 5 Jul at the Poza Rica Experiment Station, Puebla, Mexico. Twenty four treatments were replicated 4 times in a randomized complete block design. Plot size was 6 rows (0.75 m apart) × 5.0 m. Corn was thinned to 40,404 plants per hectare. All rows were infested, but only the four central ones were treated and evaluated. An avg of 26.4 larvae/plant were initially applied on 18 Jul when the crop was at the 3 expanded leaf stage. On 1 Aug the crop was reinfested at the 7-8 expanded leaf stage with an avg of 21 larvae/plant. The insecticides were applied on 24 Jul with corn at the 5.5 leaves stage. Liquid formulations were applied with a bicycle compressed air sprayer, using 8004 nozzles, 2.8 kg/cm2 and delivering 483 liters/ha. Granular formulations were applied with hand applicators, delivering 0.2 cc/stroke. Evaluations consisted of: a) Number of total and undamaged plants, at three intervals: one week after initial infestation, one week after treatment application ;md one week after reinfestation; b) Plant and ear height, on 12 Sep; c) Number of harvested plants and ears, and grain yield (15% moisture) on 24 Oct.