Leaf Disc Test Research Articles

The effect of natural herbicide from Fusarium equiseti crude extract on the aquatic weed water hyacinth (Eichornia crassipes (Mart.) Solms)

In this study, Fusarium equiseti was isolated from the weed plant Tridax procumbens in an agricultural field and a crude extract produced with 75% ethanol for use as active ingredient material in natural herbicides. The herbicidal effect of F. equiseti extract was tested on water hyacinth (Eichornia crassipes), an invasive aquatic weed, by leaf disk assay at concentrations of 0.05%, 0.1%, and 0.2% w/v crude extract. Dose-dependent visual toxicity symptoms were evident after three days, namely chlorosis, yellow leaves surrounded by dark brown edges. Photosynthetic pigments (chlorophyll a, b, and carotenoids) and membrane integrity (as electrolyte leakage and malondialdehyde content) were evaluated following the leaf disk test. 3 days after treatment, photosynthetic pigment contents showed dose-dependent decreases, while both measures of membrane integrity showed dose-dependent increases with increasing extract concentration. In addition, a cytogenetic assay was conducted on Allium cepa L. root, in which mitotic index reduction and depigmentation were evident as early as 24 h after herbicide application. Finally, anatomical analysis of treated E. crassipes leaves revealed degradation or damage of the ground tissue. All told, our results support the F. equiseti crude-based natural herbicide cloud as a sustainable alternative in agriculture.

Morphological and chemical plant traits associated with feeding non-preference to adult of Diabrotica speciosa (Coleoptera: Chrysomelidae) in soybean genotypes.

Diabrotica speciosa is an important pest of several crops in South America, including soybeans. Adults cause severe defoliation in soybean plants, and damage is significant when cotyledons are attacked. This study evaluated feeding non-preference to D. speciosa adults using 10 soybean genotypes, testing (i) 15-day-old whole plants and (ii) leaf disks of 60-day-old plants, through assessments of soybean attractiveness and leaf area consumed (LAC). Foliar contents of flavonoids and nutrients, and leaf trichome density were quantified for potential correlations with soybean resistance to adult of D. speciosa. In the whole young-plant experiment, under free-choice conditions, the lowest LAC was observed in IAC 100 and PI 227687. In no-choice, PI 227687 and IGRA RA 626 RR showed lower LAC than the other genotypes. In the leaf disk test, in free-choice, the genotypes IAC 100, PI 274454, PI 227687, DM 339, and BR 16 were the least preferred by adult of D. speciosa. In no-choice, PI 274454 was one of the least preferred, similarly to IGRA RA 626 RR, Dowling, and PI 227687. In the whole plant experiment, a high rutin content and low amounts of zinc, calcium, sulfur and manganese were associated with less consumption of D. speciosa on leaves of resistant genotypes. In contrast, in the leaf disk test there was a significant influence of trichomes in soybean resistance to the pest. In conclusion, the PI lines herein assessed are also promising sources for developing cultivars resistant to D. speciosa.

First report of the occurrence of multiple resistance to Flutianil and Pyriofenone in field isolates of Podosphaera xanthii, the causal fungus of cucumber powdery mildew

Two new fungicides, flutianil and pyriofenone were introduced into the Japanese market in 2013 and 2014, to control powdery mildew on cucumber. Isolates of Podosphaera xanthii, the causal agent of powdery mildew, were collected in Ibaraki Prefecture, Japan, between 2017 and 2019 from cucumber greenhouses with a history of flutianil and pyriofenone usage. They were then tested for sensitivity to both fungicides by the leaf disc test. First, the sensitivity of three baseline reference isolates to each fungicide was determined. Minimum inhibitory concentrations values were 0.0063 μg/ml for flutianil and 10 μg/ml for pyriofenone, while 50% effective concentration (EC50) values of these fungicides were 0.00013–0.00035 μg/ml and 0.39–0.70 μg/ml, respectively. To determine the current sensitivity of P. xanthii in detail, 23 single-spore isolates were then sampled from five greenhouses and tested. Nineteen isolates showed high resistance (Flu-HR/Pyr-HR) with EC50 values of >100 μg/ml for flutianil and > 1000 μg/ml for pyriofenone. The low sensitivity of Flu-HR/Pyr-HR isolates was stable even after 46 subcultures on fungicide-untreated cotyledons. Additionally, two isolates showed moderate resistance (Flu-MR/Pyr-MR) to flutianil (EC50: mean 0.8 μg/ml) and pyriofenone (mean 58.7 μg/ml). The results from foliar inoculation tests on potted cucumber plants confirmed low efficacies of flutianil and pyriofenone against resistant isolates. Among a total of 122 isolates sampled from 13 greenhouses, 89 isolates (73.0%) were categorized as Flu-HR/Pyr-HR and two isolates (1.6%) as Flu-MR/Pyr-MR. This is the first report on flutianil resistance in any pathogen.

Feeding preference of Altica deserticola for leaves of Glycyrrhiza glabra and G. uralensis and its mechanism

Altica deserticola (Coleoptera: Chrysomelidae) is a monophagous insect that feeds on, and is thus a harmful pest of, liquorice. Both adults and larvae feed on leaves, causing serious damage to leaf blades. It will even lead to the extinction of liquorice, resulting in significant economic losses. Leaf-disc tests were used to determine the feeding preference of A. deserticola on leaves of Glycyrrhiza uralensis and G. glabra and explore the underlying mechanism of liquorice feeding resistance to A. deserticola by comparing leaf hardness and thickness, cuticle thickness, and nitrogen and tannin content in the two plants. The results showed that larvae and adults have the same feeding preferences, i.e., both preferably fed on G. uralensis, indicating a higher resistance in this species. The hardness, thickness, and the thickness of the stratum corneum of the leaves of G. glabra were significantly greater than those of G. uralensis. Nitrogen content was higher in G. uralensis, while total tannin, tannic acid, and catechin content were higher in G. glabra. The thick cuticle and hard texture of G. glabra leaves may be an important physical trait for effectively resisting A. deserticola feeding, while high tannin and low nitrogen content may also be important.

The Synergy Effect of Azadirachtin and Minor Components of Neem Seed Oil on Antifeedant Activity of Spodoptera litura

Azadirachtin in neem oil ( Azadirachta indica A.Juss ) might have potential synergism effect with a minor compound in the neem oil as an antifeedant. This study aimed to determine the content of minor components that have the most significant contribution to the effect of synergy with the main component (azadirachtin) in antifeedant activity against Spodoptera litura . Neem oil was fractionated with n-hexane, ethyl acetate, and water. The antifeedant activity of three neem oil fractions was evaluated using the 4 th instar of S. litura larvae. The bioassay was conducted using the choice leaf disc test with 2.5; 5; 10; and 20 % (v/v) concentrations of each fraction. The concentration of the fractions showed equal azadirachtin content, hence the antifeedant activity represented the effect of the minor component in the fraction. The best activity was shown by water fraction (84-100 %). Probit analysis of the antifeedant activity of all fractions showed that water fraction has the best effective inhibitory (EI 50 ) at 1.0 %. The minor component in the water fraction was dominated by phenol compounds (48.5 %) which were suspected to synergize with the main component (azadirachtin) in increasing the antifeedant activity on S. litura . These results indicated the phenol compound in this fraction has the role in increasing azadirachtin antifeedant activity against S. litura .

Inheritance of foliar resistance to Phytophthora species in cacao (Theobroma cacao L.): can it be influenced by CSSV infection?

Studies on quantitative genetics of foliar resistance to black pod disease in cacao could inadvertently use cocoa swollen shoot virus (CSSV) infected leaves which could bias the results especially in West Africa where the virus is prevalent. However, effects of CSSV on inheritance and heritability of foliar resistance to Phytophthora species is not known. Choice of an efficient breeding method requires an accurate estimation of genetic effects in selection schemes for foliar resistance to Phytophthora species in cacao. The objective of this study was to investigate the effect of CSSV infection on quantitative genetic parameters of foliar resistance to cocoa black pod disease in a population of 36 F1 hybrids developed by mating six cacao genotypes using a diallel method. The generated F1s and their parents were evaluated for foliar resistance to P. palmivora and P. megakarya using a randomized complete block design (RCBD) with three replications. 1A CSSV and Nsaba CSSV strains were used to infect the cacao genotypes using the patch graft method. The parents chosen showed significant variations for scores of leaf discs after inoculation with P. palmivora and P. megakarya. The leaf disc scores of CSSV infected crosses were lower than leaf disc scores of CSSV-free crosses. Genetic component analysis showed that the effects of GCA and SCA was significant for both CSSV-free and CSSV-infected crosses in resistance to P. palmivora and P. megakarya. The significant GCA and SCA for both CSSV-free and CSSV-infected crosses strongly suggest that both additive and non-additive genetic effects play an important role in the determination of inheritance of foliar resistance to Phytophthora species in cacao. There was significant variability in mean squares of GCA and SCA of CSSV-free and CSSV-infected crosses indicating that CSSV infection modifies GCA and SCA of affected plants. Narrow sense heritability was relatively low (0.31) for foliar resistance to P. palmivora and P. megakarya under CSSV-free and 1A CSSV strain infected conditions. However, heritability for foliar resistance to P. palmivora (0.43) and P. megakarya (0.36) was significantly higher under Nsaba CSSV infected condition. The modifications of mean squares of GCA and SCA and narrow sense heritability due to CSSV infection could mislead in choice of breeding methods indicating that attention must be paid to the infection status of plants when conducting quantitative genetics studies using diseased and healthy plants. CSSV status of leaf samples should be known before using them in leaf disc test. Genotypes Pa7/808 and Pound 7 had high negative GCA effects and are promising parents for enhancement of resistance to black pod disease in cacao.

Transformation of Mungbean Plants for Salt and Drought Tolerance by introducing a gene for an osmoprotectant glycine betaine

Mungbean (<em>Vignaradiata</em>L. Wilczek) is an important grain legume widely cultivated in tropical and subtropical regions of the Indian subcontinent and in South East Asian countries. Protein and carbohydrate of Mungbean are easily digestible and create less flatulence than proteins derived from other legumes.Mungbean is very sensitive to salinity, drought, high and low temperature during the flowering and seed/pod development stages resulting in heavy losses to productivity. The development of genetically engineered plants by the introduction and/or over expression of selected abiotic stress tolerant genes seems to be a viable option for obtaining improved plants. Stable transformation and expression of transgene (<em>codA</em> gene) was achieved in mungbean through <em>Agrobacterium tumefaciens</em>mediated system using cotyledonary node explants, under the optimized conditions. Molecular analysis of transgenic plants was done by using PCR, DOT-BLOT, ELISA and Western blotting. The primary transformants were checked for salt tolerance by the leaf disc test.

Evaluation of botanical and chemical products for the control of foliar nematodes Aphelenchoides fragariae

Foliar nematodes Aphelenchoides spp. Pose a serious threat to floriculture by causing significant economic losses in home gardens, production nurseries and arboretums, and threatening precious germplasm collections of many ornamental plants. Control of foliar nematodes has become difficult due to the loss of nematicides following the implementation of the U.S. Food Quality Protection Act. Herein, we used a three-stage approach to evaluate 24 products for their potential to control foliar nematodes Aphelenchoides fragariae in hosta. We first performed a direct contact assay in well-plates where A. fragariae nematodes were exposed to the aqueous suspension of high (2-fold dilution) or low (20-fold dilution) concentration of the test products. The products causing 100% nematode mortality at the low concentration were then tested through a drench application for their effectiveness against foliar nematodes in soil, followed by a leaf-disc test to determine their efficacy against nematodes in leaves as a spray application. Of the 24 products, Ammonia, Clorox, grapefruit seed extract, KMnO4, NaDCC, Nemakill, Pylon and ZeroTol caused 100% nematode mortality in aqueous suspension at 20-fold dilution. Drench application of Ammonia, Clorox, KMnO4, NaDCC and ZeroTol reduced over 85% and over 75% A. fragariae population in soil 7 and 42 days after treatment, respectively. Spray application of ZeroTol could reduce over 70% A. fragariae population in leaf discs, whereas Ammonia, Clorox, KMnO4 and NaDCC caused about 50% reduction. Pylon (24% chlorfenapyr) and Nemakill (32% cinnamon oil, 8% clove oil, 15% thyme oil mixture) showed 100% mortality of A. fragariae in all three types of tests, and thus have great potential to serve as effective alternatives to manage foliar nematodes in floriculture.

Sensitivity, resistance stability, and cross-resistance of Plasmopara viticola to four different fungicides

Baseline sensitivity to fungicides was determined in 105 Plasmopara viticola isolates using the floating leaf disk test. The mean EC50 values were 0.372 ± 0.104, 0.604 ± 0.215, 0.306 ± 0.101, and 0.922 ± 0.209 μg mL−1 for fluxapyroxad, benthiavalicarb-isopropyl, ametoctradin, and famoxadone, respectively, which we regarded as the baseline sensitivity to the four fungicides. Resistant mutants can be generated using a median effective concentration or a minimum inhibitory concentration to fluxapyroxad, benthiavalicarb-isopropyl, ametoctradin, and famoxadone respectively, but the resistance stability of resistant mutants from the minimum inhibitory concentration (MIC) was significantly lower than that from the median effective concentration (EC50). In brief, high resistant mutants obtained was at the higher concentration, the resistance stability of the mutants recovered was more quickly. But lower resistant mutants obtained was at the lower concentration, the resistance stability of the mutants recovered was slower. Even if the resistance level of the mutants is low, it is more capable of stably heritable. These data indicate that the highest dosage is not used, resistance will still develop. In a correlation analysis, no cross-resistance to each other of these four fungicides was observed.

Evaluation of wild tomato accessions (Solanum spp.) for resistance to two-spotted spider mite (Tetranychus urticae Koch) based on trichome type and acylsugar content

Tomato wild relatives are important sources of resistance to many pests of cultivated tomato [Solanum lycopersicum L. (syn. Lycopersicon esculentum Mill.)]. Eleven wild tomato accessions previously identified at AVRDC—The World Vegetable Center as resistant to Bemisia tabaci were evaluated for resistance to the two-spotted spider mite [Tetranychus urticae (Koch.)] based on egg numbers using the leaf disc and Tanglefoot no-choice bioassays, and damage scores in choice bioassays. Highest resistance based on choice and no-choice bioassays was identified in AVRDC S. galapagense accessions VI057400, VI045262, VI037869 and VI037239, and S. cheesmaniae accession VI037240, all of which are new sources of T. urticae resistance. In addition, S. pimpinellifolium accession VI030462 exhibited resistance only in the no-choice bioassay based on egg numbers. Resistance to T. urticae based on the number of eggs from the no-choice bioassays was positively correlated with density of type IV glandular trichomes and negatively correlated with densities of type V trichomes. All resistant accessions accumulated high levels of total acylsugars, which were positively associated with type IV trichomes. There was a significant negative relationship between acylsugar content and T. urticae egg numbers from the no-choice bioassays. There was high correlation between the results from the leaf disc test and the Tanglefoot no-choice bioassay. These findings support the possible presence of broad-based insect and mite resistance in accessions closely related to cultivated tomato.

An Extended Leaf Disc Test for Virulence Assessment in Plasmopara Viticola and Detection of Downy Mildew Resistance in Vitis

Viticulture is continuously suffering significant economic loss from downy mildew epidemics. Although the infection biology of the pathogen Plasmopara viticola is well understood, little is known regarding the population diversity of this oomycete and on the mechanisms responsible for compatible or incompatible reactions with different host genotypes. The discrimination of strains with different virulence is a fundamental step for the assessment of pathotypes in local populations and could help to develop measures for preventing economic loss. We here describe an extended and slightly modified bioassay for the assessment of virulence by means of sporulation intensity. Simultaneously, the necrotic reaction of host genotypes is considered and allows identification of different resistance strategies. Comparison of infections symptoms of 12 host genotypes after inoculation with five different single sporangium strains of Plasmopara viticola showed that: 1. resistance diversity is high in some Vitis vinifera. Cultivars; 2. Vitis riparia showed the strongest resistance amongst the four tested North American species; 3. Asian Vitaceae harbor fully resistant as well as highly susceptible genotypes. In addition, microscopic investigation of inoculated leaf discs from Vitis amurensis and Ampelopsis japonica unraveled, that despite lack of sporulation, a mycelium may grow to a certain point in resistant hosts. The necrotic reaction in V. amurensis indicates a different mechanism of resistance when compared to A. japonica, where no necrosis was found.

Anti-feeding activity of total ginsenoside from Panax ginseng to 4th-instar Mythimna separata larvae

This paper is in order to study the anti-feeding and growth inhibition activity of toatal ginsenoside of ginseng stems and leaves against 4th-instar Mythimna separata larvae. Simulating natural growing condition indoors, on the base, To study the anti-feeding and growth inhibition activity of toatal ginsenoside against 4th-instar M. separata larvae by leaf disc test. The toatal ginsenoside appeared to be of significant antifeeding activity against 4th-instar M. separata larvae. The 4th-instar M. separata larvae fed on the leaves of Sorghum bicolor treated with 20, 10, 5 g · L(-1) toatal ginsenoside. At 8 h, non-selective anti-feeding rate were 88.67%, 64.40% and 47.36%, and selective anti-feeding rate were 62.49% , 44.29% and 34.19%; Compared with the photographic, The toatal ginsenoside conld make the development period had prolonged 13h in treated group. The toatal ginsenoside had significant inhibition effect on feeding and growth and development against 4th-instar M. separata larvae, and inhibition effect increases as the increase of concentration ginsenoside.

Development of Two New Zantedeschia Cultivars Resistant to Bacterial Soft Rot

Calla lily is a mainstream floricultural crop but its commercial success is limited by severe susceptibility to soft rot. This disease can be controlled to some extent by implementing appropriate cultural practices but developing resistant cultivars against this pathogen is the most promising long-term strategy. The purpose of this work was to develop new cultivars resistant to this bacterial disease by initiating an appropriate breeding programme. Field observations of 120 resistant lines selected by a leaf-disk susceptibility test were carried out and survival rates were measured. Two lines were selected after further evaluation of resistance level, flowering characteristics and following guidelines for conduct of tests for distinctness, homogeneity, and stability. Further preference testing of the selected lines by growers, consumers, researchers and agricultural advisors was carried out with excellent results. The selected new lines are ‘Silky White’ and ‘Mont Blanc’ which emerge as the first, soft-rot resistant calla lily cultivars from our breeding program.

Efficacy Assessment of Different Screening Methods for Detecting Resistance against Erwinia carotovora in Calla Lily

Bacterial soft rot is one of the major disease of Zantedeschia species (Calla lily) caused by Erwinia carotovora. The objectives of this study were i) to screen the most efficient method to determine resistance level against E. carotovora and ii) to evaluate the genetic variability in Zantedeschia genotypes by inoculation of Ecc NHRI-3 and PD 1784 isolates. Four screening tests i.e. leaf disk, petiole, tuber and tuber slice tests were used to determine the resistance level in calla lily. Eleven genotypes from section Zantedeschia were used for variation studies against E. carotovora by using the leaf disk test. It was observed that all genotypes showed variation in resistance level and could be categorized in 3 groups on the basis of their resistance level. Four of the genotypes were resistant against this pathogen whereas, 6 genotypes were moderately resistant and only one genotype was found susceptible. Within section Aestivae, ‘Galaxy’, ‘Florex Gold’, ‘Treasure’ and ‘Mango’ were found very susceptible cultivars, whereas ‘Coral Sunset’, ‘Hazel Marie’ and ‘Neroli’ were less susceptible genotypes. Most of the cultivars from section Aestivae were susceptible to bacterial soft rot and the cultivar ‘Florex Gold’ was identified as susceptible control. It is suggested to perform pre-screening through leaf disk method which proved to a non-destructive test. The pre-screening evaluation can discriminate susceptible cultivar and resistant cultivar. Tuber slice test is more useful in screening subsequent genotypes at a later growth stage in any breeding program.

RETRACTED ARTICLE: Effect of calcium and silicate application on pathogenicity of Erwinia carotovora subsp. carotovora in Zantedeschia spp.

The purpose of this study was to evaluate the effects of calcium and silicate on plant growth and resistance to Erwinia carotovora subsp. carotovora in Zantedeschia aethiopica ‘Childsiana’. Calcium and silicate as basal fertilizer (mixed with soil before cultivation) were applied at 0, 100, 200, or 400 kg·10 a−1, respectively. Potassium silicate (K2O·nSiO2) and CaCl2 foliar application were applied 3 times every 2 weeks at 0, 0.05, 0.1, or 0.2%, respectively at the middle stage of growth on the Zantedeschia. The level of resistant to Erwinia carotovora subsp. carotovora was tested by leaf disk test at blooming stage. The higher concentration of calcium and silicate in the foliar application and basal application resulted in vigorous leaf growth, hardness of petiole and flower stalk and in fresh weight. The resistance to Erwinia carotovora subsp. carotovora was more effective in CaCl2 foliar treatment than the basal fertilization treatment. Foliar treatment at 0.2% CaCl2 was the most effective against the resistance of Erwinia carotovara subsp. carotovora. Also, the level of resistant to Erwinia carotovora subsp. carotovora was higher in proportion to the silicate application rate both in foliar and basal application of fertilizer. In the analysis of SEM, it was observed that at high concentration of silicate there was more accumulates of Si between cell wall, vascular bundle, and companion cell around sieve tube element. It was consistent with the result of hardness of petiole and flower stalk.

Inheritance of downy mildew resistance at different developmental stages in Chinese cabbage via the leaf disk test

Downy mildew, caused by Hyaloperonospora parasitica, is a destructive disease of the Chinese cabbage (Brassica rapa ssp. pekinensis). A rapid resistance/susceptibility test for H. parasitica was established by the inoculation of a leaf disk test. Four conditions were tested and the optimal condition was found when the inoculated leaf disk was placed into dark conditions at 16°C for the first 24 hours after inoculation, followed by 5 days of light at 20 and 23°C for 4 hours and 5 hours, respectively, dark at 16°C and 12°C for 3 hours and 12 hours, respectively, and a final temperature of 16°C for 24 hours. There was a good correlation between the resistance levels of leaf disks and the resistance of seedlings or adult plants, which indicated that testing leaf disks should be the preferred methods to predict the resistance of adult plants. Using this method, downy mildew resistance was investigated in a double haploid (DH) population at four developmental stages. The results showed that the genetic pattern, which was deduced from the DH segregation, was relatively similar, but varied slightly during plant development.

Resistance to Bemisia tabaci in tomato wild relatives

AbstractBemisia tabaci is one of the most threatening pests in agriculture, particularly in Solanaceous crops such as tomato and pepper that are cultivated in the open field. Pesticide application is often not effective and hazardous to humans and environment. The exploitation of plant natural defenses that are present in wild relatives of tomato, may offer a solution. To evaluate resistance parameters and to identify plant material with high levels of resistance, we screened a number of accessions of tomato wild relatives using three methods; a free-choice test in a screenhouse in Indonesia, a no-choice test with clip-on cages in a greenhouse and a leaf disc test in a climate-room in the Netherlands. Antibiosis resulting in low adult survival was the major component for resistance in tomato. However, other resistance component(s) may play a role as well. In some accessions there was a change in the resistance level over time. Several resistance parameters used in the different tests were well correlated. The best resistance source was an accession of Solanum galapagense, which had not been identified as being resistant in the past. This is of particular interest as this species is closely related to the cultivated tomato, which may facilitate introgression of the resistance component(s). Whitefly non-preference and resistance were associated with the presence of type IV trichomes. Other mechanisms might be involved since some accessions without type IV trichomes showed low nymphal density. The leaf disc test is a good in vitro alternative for the clip-on cage whitefly resistance screening, as shown by the high correlation between the results obtained with this test and the clip-on cage test. This offers breeders the possibility to carry out tests more efficiently.

Acaricidal activity and repellency of essential oil from Piper aduncum and its components against Tetranychus urticae

The chemical composition of essential oil of leaves of Piper aduncum L., growing wild in a fragment of the Atlantic Rainforest biome in northeastern Brazil, was determined through gas chromatography-mass spectrometry. The acaricidal activity and repellency of the essential oil and its components [dillapiole (0.28 g/ml), α-humulene (0.016 g/ml), (E)-nerolidol (0.0007 g/ml) and β-caryophyllene (0.0021 g/ml)] were evaluated in the laboratory against adults of Tetranychus urticae Koch. The mites were more susceptible to the oil in fumigation tests (LC(50) = 0.01 μl/l of air) than in contact test with closed Petri dish (LC(50) = 7.17 μl/ml); mortality was reduced by approximately 50 % in the latter test. The repellent action of the oil and toxicity by fumigation and contact did not differ significantly from the positive control (eugenol). The repellent activity was attributed to the components (E)-nerolidol, α-humulene and β-caryophyllene, whereas toxicity by fumigation and contact was attributed to β-caryophyllene. The effect of Piper oil and the role of its components regarding host plant preference with a two-choice leaf disk test are also discussed.

Resistance gradient of black pod disease in cocoa and selection by leaf disk assay

To characterize the gradient of resistance to black pod disease experimentally, the leaf disk assay was applied to 217 cocoa genotypes. The parameters time interval, number of leaves evaluated per genotype and distribution of experimental treatments were evaluated. Significant differences between genotypes were found, resulting in the grouping in five homogenous groups (p < 0.01). In the assessments with the leaf disk test, five and seven days after inoculation, the F value was highest after seven days, clearly separating the resistant from susceptible genotypes. There was no difference between the clones behavior and the use of more than one box to group the genotypes (p = 0.56) and the use of different leaves of the same genotype (p = 0.08). The resistance gradient observed indicates variability enough for mapping and cocoa breeding in the population.

Host Plant and Leaf-Age Preference ofLuprops tristis(Coleoptera: Tenebrionidae: Lagriinae: Lupropini): A Home Invading Nuisance Pest in Rubber Plantation Belts

Massive seasonal invasion by the litter-dwelling beetleLuprops tristis, into residential buildings prior to monsoon rains, and their prolonged state of dormancy render them a very serious nuisance pest in rubber plantations in the Western Ghats in southern India. Feeding preferences ofL. trististowards leaf litter of seven trees co-occurring in rubber plantations, cashew (Anacardium occidentale), mango (Mangifera indica), jackfruit (Artocarpus heterophyllus), wild jack (Artocarpus hirsutus), cocoa (Theobroma cacao), cassia (Cassia fistula), sapota (Manilkara zapota) and rubber (Hevea brasiliensis) were analyzed with no-choice and multiple-choice leaf disc tests. Results showed thatL. tristisis a generalist feeder with a defined pattern of preference, with the leaf litter of rubber being the most preferred followed by those of jackfruit and cocoa. Tender leaves were preferred over mature leaves except for cocoa and sapota. Equal preference towards tender and mature cocoa leaves, presence of patches of cocoa plantations and the scarce distribution of other host plants in rubber plantation belts leads to the proposal that in the absence of tender and mature rubber leaves, cocoa becomes the major host plant ofL. tristis.