Early Plant Vigour Research Articles

Presowing Mechanical Seed Treatment Influencing the Emergence and Primary Seedling Vigor of Jujube (Ziziphus mauritiana Lam.)

Rootstock preparation from seed is the prerequisite for fruit crop multiplication through grafting or budding, and hard seed coat in jujube has been the proven question for uniform seed germination and subsequent seedling growth. Therefore, the study aimed at successful and rapid production of uniform and healthy jujube rootstocks through applying mechanical seed priming at the presowing stage. The experiment was set in a randomized complete block design where scrapped seeds, cracked seeds, seed kernels, and intact seeds (control) were sown in polybags keeping five replications. The emergence and initial seedling growth were evaluated to sort out the best pretreatment methods for successful stock seedling production in jujube. Seed cracking resulted in the highest germination (69.00%) compared to other pretreatments and also showed better performance in respect of earliness of emergence (10.40 days (d) for the first emergence and 20.40 d for final emergence). Regarding the early plant vigor, significantly maximum seedling height (23.73 cm) and fresh (3.91 g) and dry weight (1.17 g) of seedling and the second‐best leaf number (14.24 seedling−1) were also noted in seed cracking. Although seed kernel had the fastest emergence in 7.20 d, and statistically similar seedling vigor with that of cracked seed but it possessed very low germination percentage (27.00%) compared to the best treatment. Meanwhile, seed priming by scrapping exhibited statistically inferior germination rate (32%) as of intact seed (21%), and below par seedling growth compared to cracked seed. So, seed pretreatment by cracking can be suggested for commercial stock plant regeneration in hard seed‐coated plant species.

Agronomic strategies to enhance the early vigor and yield of maize part II: the role of seed applied biostimulant, hybrid, and starter fertilization on crop performance.

Maize cropping systems need to be re-designed, within a sustainable intensification context, by focusing on the application of high-use efficiency crop practices, such as those that are able to enhance an early plant vigor in the first critical growth stages; such practices could lead to significant agronomic and yield benefits. The aim of this study has been to evaluate the effects of the cultivation of hybrids with superior early vigor, of the distribution of starter fertilizers at sowing, and of the seed application of biostimulants on promoting plant growth and grain yield in full factorial experiments carried out in both a growth chamber and in open fields. The greatest benefits, in terms of plant growth enhancement (plant height, biomass, leaf area) and cold stress mitigation, were detected for the starter fertilization, followed by the use of an early vigor hybrid and a biostimulant seed treatment. The starter fertilization and the early vigor hybrid led to earlier flowering dates, that is, of 2.1 and 2.8 days, respectively, and significantly reduced grain moisture at harvest. Moreover, the early vigor hybrid, the starter NP fertilization, and the biostimulant treatment increased grain yield by 8.5%, 6.0%, and 5.1%, respectively, compared to the standard hybrid and the untreated controls. The combination of all the considered factors resulted in the maximum benefits, compared to the control cropping system, with an increase in the plant growth of 124%, a reduction of the sowing-flowering period of 5 days, and a gain in grain yield of 14%. When choosing the most suitable crop practice, the diversity of each cropping system should be considered, according to the pedo-climatic conditions, the agronomic background, the yield potential, and the supply chain requirements.

Genetic mapping and transcriptome profiling of a chickpea (Cicer arietinum L.) mutant identifies a novel locus (CaEl) regulating organ size and early vigor.

Chickpea is among the top three legumes produced and consumed worldwide. Early plant vigor, characterized by good germination and rapid seedling growth, is an important agronomic trait in many crops including chickpea, and shows a positive correlation with seed size. In this study, we report a gamma-ray-induced chickpea mutant with a larger organ and seed size. The mutant (elm) exhibits increased early vigor and contains higher proline that contributes to a better tolerance under salt stress at germination, seedling, and early vegetative phase. The trait is governed as monogenic recessive, with wild-type allele being incompletely dominant over the mutant. Genetic mapping of this locus (CaEl) identified it as a previously uncharacterized gene (101503252) in chromosome 1 of the chickpea genome. There is a deletion of this gene in the mutant with a complete loss of expression. In silico analysis suggests that the gene is present as a single copy in chickpea and related legumes of the galegoid clade. In the mutant, cell division and expansion are affected. Transcriptome profiling identified differentially regulated transcripts related to cell division, expansion, cell wall organization, and metabolism in the mutant. The mutant can be exploited in chickpea breeding programs for increasing plant vigor and seed size.

Development and characterization of F1 hybrids involving cultivated and related species of okra

Related species of any crop posses the traits of economic importance. It is important to involve the related wild species in the breeding programme to transfer the traits of economic importance to the cultivated species of crop plants. Further, the characterization of interspecific F1 hybrids is required to know the expression of various traits in both parents and their interspecific hybrid. Cultivated species of okra Abelmoschus esculentus was used to develop two interspecific F1 hybrids independently with two wild species, namely A. moschatus and A. tuberculatus. Both the related species were used as the pollen parent and the cultivated okra as the female parent. The interspecific hybrids were intermediate for days to 50% flowering, first flowering node, flower length, fruit length, fruit diameter, internodal length and plant height. The characteristics like early plant vigor, plant growth habit, flower petal color, fruit color and apex shape of fruit for both the interspecific hybrids were similar to cultivated okra parent.

A multi‐environment analysis of winter faba bean germplasm for cover crop traits

AbstractFaba bean (Vicia faba L.) cultivars for cover cropping have remained unchanged in the western United States over the past century. Although breeding efforts have improved grain production across much of the world, improvement of the crop for cover crop applications (e.g., biomass production at the flowering stage) remains understudied. Therefore, a trial of nine newly developed faba bean lines from the USDA‐ARS and four commercial checks (‘Bell Bean’, ‘V4’, ‘V5’, and ‘Windsor’) was established to evaluate cover crop traits across six diverse testing environments. The experiment revealed significant genotype × environment interactions for winter vigor, nitrogen (N) concentration, and aboveground N yield. Significant genotypic variation was observed for important cover crop traits including winter vigor, spring vigor, aboveground biomass, and aboveground N yield, whereas variation for percentage of N derived from the atmosphere was primarily determined by the testing environment. The study also identified a strong association between early plant vigor and aboveground biomass (r = .71), which offers potential increases in breeding efficiencies. In addition, advanced faba bean lines from the USDA‐ARS were shown to produce twice the biomass of Bell Bean across testing environments, and faba bean line PS18301 produced at least 20% more aboveground N yield in five out of the six environments than the conventionally used cover crop cultivars Windsor and Bell Bean. Faba bean lines in this study may be used by cover crop breeders as parent materials.

Soil disturbance levels, soil water content and the establishment of rainfed chickpea: Mechanised seeding options for smallholder farms in north‐west Bangladesh

AbstractOptimum soil physical conditions for crop establishment are more likely to occur with mechanised row‐sowing using metered seeding and controlled depth placement of seeds than with broadcast sowing, that is common in many traditional South Asian cropping practices. Establishment success is a limitation for post‐rice crops in medium to heavy textured soils in the Eastern Gangetic Plain because sowing coincides with rapid topsoil drying and increases in soil strength. In addition, due to lack of rainfall in the post‐rice season the crop relies on access to stored soil water during vegetative and reproductive growth to achieve adequate yields. Our aim was to determine whether decreased soil disturbance (from full tillage to zero tillage (ZT) to undisturbed soil (Fallow)) and direct seeding (using small‐scale seeders) could 1) enhance chickpea crop establishment by conserving seedbed soil water and 2) alter crop water use of the water stored in the soil profile. The silt loam soil has an estimated volumetric soil water content (θv) of 34% at field capacity. At sowing, θv in the seedbed was between 25% to 29%. This was adequate for successful chickpea crop establishment, but slightly wetter than optimum for tillage. In the wet soil at sowing, there was evidence of smeared furrow walls and poor soil covering of the seed in the seedbed in strip planting (SP; rotating blades in front of tine) and ZT. Uncovered furrows (in ZT; using a tine opener) and the fallow soil lost more surface soil water (9%, 23 days after sowing) than the seedbeds created with greater levels of soil disturbance. In 2008, grain yield of single‐pass shallow tillage (SPST) was greater than SP but in 2009, grain yields of all one‐pass tillage techniques (ZT, SP, SPST) were greater than in the broadcast seeding in fully tilled soils. The improvement in chickpea yields was attributed to greater plant numbers, early plant vigour and root growth. Chickpea roots were found to 60 cm depth in the soil profile, and soil water content was less than the θv of wilting point to this depth at podding. There is evidence that root growth and plant water uptake occur deeper in these soil profiles to achieve the grain yields > 1,000 kg/ha recorded in this study. Mechanised sowing in rows with small‐scale seeders has the capability to overcome establishment and yield limitations for chickpea on medium to heavy soils in the post‐rice season.

Identification of genomic regions associated with early plant vigour in lentil (Lens culinaris)

Lentil is one of the most important food legume species, however its genetic and genomic resources remained largely uncharacterized and unexploited. In the past few years, a number of genetic maps have been constructed and marker resources have been developed in lentil. These resources could be exploited for understanding the extent and distribution of genetic variation in genus Lens and also for developing saturated and consensus genetic maps suitable for quantitative trait loci (QTL) mapping and marker-assisted selection. The present study aims to enrich polymerase chain reaction-based linkage map of F10 recombinant inbred lines (RILs) population of 94 individuals derived from cross WA8649090 9 Precoz and identification of QTLs linked to early plant vigour traits. Of the 268 polymorphic markers (93 simple sequence repeats (SSR), three inter-simple sequence repeats (ISSRs) and 172 random amplified polymorphic DNA (RAPDs)), 265 (90 SSRs, three ISSRs and 172 RAPDs) were mapped on seven linkage groups, varying in length between 25.6 and 210.3 cM, coverage of 809.4 cM with an average marker spacing of 3.05 cM. The study also reported assigning of 24 new cross-genera SSRs of Trifolium pratense on the present linkage map. The RILs along with the parents were screened for shoot length, root length, seedling length, dry weight, number of leaves and number of branches based on two replications under polyhouse conditions. A QTLhotspot consisting of six QTLs for shoot length (cm), root length (cm) and seedling length (cm) was observed between a map distances of56.61 and 86.81 cM on LG1.

Heritability and Functional Importance of the Setaria viridis Bacterial Seed Microbiome

Seed-associated bacteria represent an important reservoir of microorganisms passed onto progeny plants and have been postulated to be important for early plant development and early plant vigor. According to a few reports, some bacterial taxa seem to be transferred from seed to seed and some seed-associated microorganisms may derive from insect visits during flowering; however, the origin of seed endophytes is poorly understood. To better understand the origin, ecology, and functional role of seed bacterial endophytes, we planted Setaria viridis seeds over several generations in a sterile growth substrate. Seed microbiota of each generation were analyzed by next generation sequencing of 16S rRNA genes and seeds were characterized regarding to their germination and plant growth. Growing plants in a sterile (or highly depleted) substrate resulted in seed microbiota, which were largely less diverse and which had altered community composition, particularly at later generations, indicating that soil is an important reservoir of seed microbiota. Some taxa were inherited to the next generations seeds; however, different subsets of taxa were inherited in different seeds/seed batches and across different generations. This suggests that other factors than the host control the establishment of most seed endophytes and only few, e.g., obligate endophytes, might be consistently inherited. Furthermore, we observed a drastic decline in seed vigor and later generations were particularly affected. Overall, our results demonstrated that the supply of endophytes from external sources such as the soil/rhizosphere environment is highly important for the build-up of a healthy seed microbiome warranting early plant establishment and vigor of next generation plants.

Evaluating RGB Imaging and Multispectral Active and Hyperspectral Passive Sensing for Assessing Early Plant Vigor in Winter Wheat.

Plant vigor is an important trait of field crops at early growth stages, influencing weed suppression, nutrient and water use efficiency and plant growth. High-throughput techniques for its evaluation are required and are promising for nutrient management in early growth stages and for detecting promising breeding material in plant phenotyping. However, spectral sensing for assessing early plant vigor in crops is limited by the strong soil background reflection. Digital imaging may provide a low-cost, easy-to-use alternative. Therefore, image segmentation for retrieving canopy cover was applied in a trial with three cultivars of winter wheat (Triticum aestivum L.) grown under two nitrogen regimes and in three sowing densities during four early plant growth stages (Zadok’s stages 14–32) in 2017. Imaging-based canopy cover was tested in correlation analysis for estimating dry weight, nitrogen uptake and nitrogen content. An active Greenseeker sensor and various established and newly developed vegetation indices and spectral unmixing from a passive hyperspectral spectrometer were used as alternative approaches and additionally tested for retrieving canopy cover. Before tillering (until Zadok’s stage 20), correlation coefficients for dry weight and nitrogen uptake with canopy cover strongly exceeded all other methods and remained on higher levels (R² > 0.60***) than from the Greenseeker measurements until tillering. From early tillering on, red edge based indices such as the NDRE and a newly extracted normalized difference index (736 nm; ~794 nm) were identified as best spectral methods for both traits whereas the Greenseeker and spectral unmixing correlated best with canopy cover. RGB-segmentation could be used as simple low-cost approach for very early growth stages until early tillering whereas the application of multispectral sensors should consider red edge bands for subsequent stages.

Chickpea Genotypes Contrasting for Vigor and Canopy Conductance Also Differ in Their Dependence on Different Water Transport Pathways.

Lower plant transpiration rate (TR) under high vapor pressure deficit (VPD) conditions and early plant vigor are proposed as major traits influencing the rate of crop water use and possibly the fitness of chickpea lines to specific terminal drought conditions—this being the major constraint limiting chickpea productivity. The physiological mechanisms underlying difference in TR under high VPD and vigor are still unresolved, and so is the link between vigor and TR. Lower TR is hypothesized to relate to hydraulic conductance differences. Experiments were conducted in both soil (Vertisol) and hydroponic culture. The assessment of the TR response to increasing VPD showed that high vigor genotypes had TR restriction under high VPD, and this was confirmed in the early vigor parent and progeny genotype (ICC 4958 and RIL 211) having lower TR than the late vigor parent and progeny genotype (ICC 1882 and RIL 022). Inhibition of water transport pathways [apoplast and symplast (aquaporins)] in intact plants led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. De-rooted shoot treatment with an aquaporin inhibitor led to a lower transpiration inhibition in the early vigor/low TR genotypes than in the late vigor/high TR genotypes. Early vigor genotypes had lower root hydraulic conductivity than late vigor/high TR genotypes. Under inhibited conditions (apoplast, symplast), root hydraulic conductivity was reduced more in the late vigor/high TR genotypes than in the early vigor/low TR genotypes. We interpret that early vigor/low TR genotypes have a lower involvement of aquaporins in water transport pathways and may also have a smaller apoplastic pathway than high TR genotypes, which could explain the transpiration restriction under high VPD and would be helpful to conserve soil water under high evaporative demand. These findings open an opportunity for breeding to tailor genotypes with different “dosage” of these traits toward adaptation to varying drought-prone environments.

Characterization of Sorghum germplasm for various qualitative traits

Present study was performed to characterize 750 germplasm lines with 4 checks namely CSV17, CSV20, CSV27 and CSV21F for various qualitative traits of Sorghum. These 754 genotypes were sown in augmented RBD with 30 replications during Kharif 2014 at Instructional Farm, Rajasthan College of Agriculture, Udaipur. Majority of the accessions showed poor early plant vigour (40.2 %), dark green leaf (88.6 %), non- tan leaf sheath pigmentation (60 %), drooping leaves (100 %), white midrib colour (51.6 %), senescence (60 %), loose panicle density (31.5 %), elliptical panicle shape (66.5 %), straw glume colour (48.2 %), 3/4 glume coverage (42.9 %), absence of awns (59.5 %), creamy straw seed (39.9 %), oval grain shape (48.8 %), medium seed size (43.7 %), non-lustrous seed (62.0 %), intermediate endosperm texture (50.3 %) and bicolor race (49.6 %). Very good early plant vigour, tan type leaf sheath pigmentation, drooping leaf orientation, straw glume colour, ½ glume covering, oval grain shape, intermediate endosperm texture appeared in all the 4 check. The results of this study indicated that considerable genetic diversity exists among the sorghum accessions.

Genetic Diversity under Soil Compaction in Wheat: Root Number as a Promising Trait for Early Plant Vigor.

Soil compaction of arable land, caused by heavy machinery constitutes a major threat to agricultural soils in industrialized countries. The degradation of soil structure due to compaction leads to decreased (macro-) porosity resulting in increased mechanical impedance, which adversely affects root growth and crop productivity. New crop cultivars, with root systems that are adapted to conditions of increased soil strength, are needed to overcome the limiting effects of soil compaction on plant growth. This study aimed (i) to quantify the genetic diversity of early root system development in wheat and to relate this to shoot development under different soil bulk densities and (ii) to test whether root numbers are suitable traits to assess the genotypic tolerance to soil compaction. Fourteen wheat genotypes were grown for 3 weeks in a growth chamber under low (1.3 g cm-3), moderate (1.45 g cm-3), and high soil bulk density (1.6 g cm-3). Using X-ray computed tomography root system development was quantified in weekly intervals, which was complemented by weekly measurements of plant height. The development of the root system, quantified via the number of axial and lateral roots was strongly correlated (0.78 < r < 0.88, p < 0.01) to the development of plant height. Furthermore, significant effects (p < 0.01) of the genotype on root system development and plant vigor traits were observed. Under moderate soil strength final axial and lateral root numbers were significantly correlated (0.57 < r < 0.84, p < 0.05) to shoot dry weight. Furthermore, broad-sense heritability of axial and lateral root number was higher than 50% and comparable to values calculated for shoot traits. Our results showed that there is genetic diversity in wheat with respect to root system responses to increased soil strength and that root numbers are suitable indicators to explain the responses and the tolerance to such conditions. Since root numbers are heritable and can be assessed at high throughput rates under laboratory and field conditions, root number is considered a promising trait for screening toward compaction tolerant varieties.

Response of Maize (Zea mays L.) Secondary Growth Parameters to Conservation Agriculture and Conventional Tillage Systems in Zimbabwe

&lt;p&gt;Previous, research focused mainly on the effects of conservation agriculture (CA) and conventional practices (CP) on crop yield mostly. A study was conducted at five sites in Zimbabwe from 2012 to 2014 to investigate effects of CA and CP practices on emergence, chlorophyll content, early vigour and grain yield of different maize varieties using 12 hybrids and 4 open pollinated varieties (OPVs). The experiment was laid as a 4 × 4 alpha lattice design with three replications. Emergence was higher under CA (75%) at University of Zimbabwe (UZ) in 2012/13 and Domboshawa Training Centre (DTC) (67%) compared to CP (71% and 39% respectively). Lower early plant vigour was observed under CA compared to CP at most sites. CA had lower leaf chlorophyll content during the early crop growth stages compared to CP. However, at some instances, CA had higher leaf chlorophyll content (45 units) than CP (35 units) at 78 days after sowing in Zimuto 2012/13. For maize yield, CA outperformed CP on a sandy loamy soil (3050 kg ha&lt;sup&gt;-1&lt;/sup&gt; vs 2656 kg ha&lt;sup&gt;-1&lt;/sup&gt;) and clay soil (4937 kg ha&lt;sup&gt;-1&lt;/sup&gt; vs 4274 kg ha&lt;sup&gt;-1&lt;/sup&gt;). However, on a sandy soil, CP outperformed CA (1764 vs 1313 kg ha&lt;sup&gt;-1&lt;/sup&gt;). Our results suggest that tillage effects on early maize plant vigor, leaf chlorophyll content and the final yield can be site and season specific. Furthermore, a delay of nutrient release for plant uptake under CA systems was found and potentially implies investigations of new fertilization strategies for such cropping systems.&lt;/p&gt;

Dynamic quantification of canopy structure to characterize early plant vigour in wheat genotypes.

Early vigour is an important physiological trait to improve establishment, water-use efficiency, and grain yield for wheat. Phenotyping large numbers of lines is challenging due to the fast growth and development of wheat seedlings. Here we developed a new photo-based workflow to monitor dynamically the growth and development of the wheat canopy of two wheat lines with a contrasting early vigour trait. Multiview images were taken using a 'vegetation stress' camera at 2 d intervals from emergence to the sixth leaf stage. Point clouds were extracted using the Multi-View Stereo and Structure From Motion (MVS-SFM) algorithm, and segmented into individual organs using the Octree method, with leaf midribs fitted using local polynomial function. Finally, phenotypic parameters were calculated from the reconstructed point cloud including: tiller and leaf number, plant height, Haun index, phyllochron, leaf length, angle, and leaf elongation rate. There was good agreement between the observed and estimated leaf length (RMSE=8.6mm, R (2)=0.98, n=322) across both lines. Significant contrasts of phenotyping parameters were observed between the two lines and were consistent with manual observations. The early vigour line had fewer tillers (2.4±0.6) and larger leaves (308.0±38.4mm and 17.1±2.7mm for leaf length and width, respectively). While the phyllochron of both lines was quite similar, the non-vigorous line had a greater Haun index (more leaves on the main stem) on any date, as the vigorous line had slower development of its first two leaves. The workflow presented in this study provides an efficient method to phenotype individual plants using a low-cost camera (an RGB camera is also suitable) and could be applied in phenotyping for applications in both simulation modelling and breeding. The rapidity and accuracy of this novel method can characterize the results of specific selection criteria (e.g. width of leaf three, number of tillers, rate of leaf appearance) that have been or can now be utilized to breed for early leaf growth and tillering in wheat.

Clustering of Greengram (Vigna radiata(L.) Wilczek) Genotypes Based on Qualitative Characters

Greengram is an important grain legume of the arid and semiarid regions. This crop has enough genetic diversity both for quantitative and qualitative characters. The qualitative traits using minimal descriptors was developed by NBPGR. Enough work had been done in characterising the greengram using quantitative characters. In this study, fifteen qualitative characters were chosen for phenotyping the 40 greengram germplasm. The fifteen characters Early plant vigour, Plant growth habit, Leaf colour, Terminal leaf length (cm), Leaflet shape, Plant surface, Branching pattern, Flower colour, Leafiness, Flowering tendency, Raceme position, Pod pubescence, Pod colour, Seed colour, Hypocotyl colour. The crop was raised in Randomised Block Design with three replications at AC & RI, Madurai during kharif 2012. The data was subjected to statistical analysis and the results revealed that 40 greengram genotypes were grouped into six clusters at 40% level. The variety ADT 1 is the distinct one differing from the other genotypes studied. It could be inferred from the present study that the geographical origin of most of the greengram germplasm is from the southern states of India having enough genetic variability in germplasm.

High-throughput phenotyping early plant vigour of winter wheat

In contrast to high-throughput genotyping which can manage a large number of plants at relatively low cost, phenotyping of many individual genotypes in field trials is still laborious and expensive. Early plant vigour, as an early selection criterion, is a trait that is visually scored due to a lack of suitable phenotyping methods for an accurate detection of this trait in large field trials. A high-throughput phenotyping technique for scoring early plant vigour would enhance the breeding process. This study was conducted to develop a method for scoring phenotypic differences in early plant vigour of 50 winter wheat (Triticum aestivum L.) cultivars in a 2-years experiment using a vehicle based multispectral active sensor and two commercially available active sensors, GreenSeeker and CropCircle. Pixel analysis of RGB images revealed to be the most feasible and superior method compared to other possible reference methods. A comparison between the two years 2011 and 2012 confirmed that early plant vigour was affected by genotypic differences. A novel spectral plant vigour index (EPVI) was found to accurately reflect the plant vigour at tillering. Different methods were applied to identify optimal combinations of wavelengths to predict early plant vigour, including multivariate modelling and prediction, contour maps for identifying all possible simple ratios and testing of combined indices. The EPVI and the relative amount of green pixels (RAGP) derived from digital images were significantly related with r2=0.98 to each other in both years. A total of 200 plots, 12m in length, could be measured within 75min. The EPVI was shown to be an accurate scoring method for the high-throughput screening of large field trials. The rapidity and accuracy of this novel method may contribute to enhanced selection at early growth stages.

Combining effects of soil solarization and grafting on plant yield and soil-borne pathogens in cucumber

Combining effects of soil solarization and grafting on soilborne pathogens, plant height and yield in cucumber were compared in a greenhouse of Bati Akdeniz Agricultural Research Institute located in Antalya in 2008 fall season. The experiment was set in split plot design containing; 1, 2, 4 and 5 months soil solarization (MSS), and non-solarized control plots (NSC) on which grafted Maximus F1+ Bergama F1 and non-grafted Bergama F1 were grown. Almost all of plants grown in non-solarized plots were infected with root-knot nematodes with severe root damages; however, only a few plants were affected by this nematode in 4 and 5 month solarized plots with very slight root galls. No resistance to root-knot nematodes was observed in both grafted and non-grafted plants. Almost half of the plants grown on non-solarized control plots were infected with Fusarium oxysporum f. sp. cucumerinum with relatively slight disease symptoms. In conclusion, combining solarization with grafting significantly promoted early flowering time, plant vigor, early and total yields and reduced nematode and fusarium wilt damages in this study.

Quantitative trait loci for early plant vigour of maize grown in chilly environments

Maize (Zea mays L.) is particularly sensitive to chilling in the early growth stages. The objective of this study was to determine quantitative trait loci (QTL) for early plant vigour of maize grown under cool and moderately warm conditions in Central Europe. A population of 720 doubled haploid (DH) lines was derived from a cross between two dent inbred lines contrasting in early vigour and were genotyped with 188 SSR markers. The DH lines per se and their testcrosses with a flint line were evaluated in field experiments across 11 environments in 2001 and 2002. Plants were harvested after six to eight leaves had been fully developed to assess fresh matter yield as a criterion of early vigour. Seven QTL were detected for line performance and ten QTL for testcross performance, explaining 64 and 49% of the genetic variance. Six out of seven QTL detected in the lines per se were also significant in their testcrosses. Significant QTL x environment interaction was observed, but no relationship existed between the size of the QTL effects and the mean temperature in the individual environment. The correlation between fresh matter yield and days to silking was non-significant, indicating that differences in early plant vigour were not simply caused by maturity differences. For three additional chilling-related traits, leaf chlorosis, leaf purpling, and frost damage seven, six, and five QTL were detected, respectively. Three QTL for leaf chlorosis, two for leaf purpling, and two for frost damage co-localized with QTL for fresh matter yield. Results are considered as a reliable basis for further genetic, molecular, and physiological investigations.

EFFECT OF RESIDUE MANAGEMENT METHODS ON NO-TILL DRILL PERFORMANCE

Excessive crop residue on the soil surface impedes drill performance and subsequent crop production inconservation tillage systems. To address this issue, 10 different residue management strategies were evaluated to determinetheir effect on no-till drill performance in terms of seedling establishment, early plant vigor, and crop yield. Field conditionswere characterized by size, concentration, and distribution of residue. Residue management strategies included leaving tallstanding stubble, using various chopping and spreading devices, and removing the residue by baling. Experiments wereconducted in northeastern Oregon fields that had been previously seeded to winter wheat and produced 9.8 and 10.5 t/ha ofresidue in 2000 and 2001, respectively. Winter and spring wheat plots were seeded with a hoe-type no-till drill. For the residuemanagement methods used in this study, stand establishment and seedling dry weight were reduced by 20% to 58% and 22%to 46%, respectively, when the full quantity of residue was left on the soil surface as compared to those where the residueconcentration was reduced by baling. Seeding into high concentrations of residue left by non-uniform residue distributionsystems also caused reductions in stand establishment and early plant growth. Long standing stubble and high concentrationsof loose straw greater than 18 cm in length caused unacceptable drill plugging. Successful drill operation was achieved incrop residues exceeding 9.8 t/ha when stubble height was less than or equal to row spacing and the majority of cut straw wascut into pieces less than 18 cm long. Although consistent yield differences were not found, the results of this study showedthat residue concentration and size have an important influence on no-till crop yield potential and drill operation.

Phytotoxicity Associated with Drip-applied 1,3-Dichloropropene and Chloropicrin in Vegetables Produced with Plastic Mulch

The effects of drip-applied 1,3-dichloropropene (1,3-D) and chloropicrin on fumigant soil gas levels and growth of vegetable seedlings were investigated in three separate tests in Tifton, Ga. Tests were conducted in Spring 2002, Fall 2002, and Spring 2003. Phytotoxicity of 1,3-D + chloropicrin was induced in the 2002 tests by applying progressively higher rates (0 to 374 L·ha–1) of drip-irrigated InLine (an emulsifiable formulation (EC) containing 60.8% 1,3-D and 33.3% chloropicrin) and planting vegetable seedlings within four days after application. Vegetables evaluated were tomato, pepper and cucumber (Spring 2002), and tomato and squash (Fall 2002). In Spring 2003, the effects of 1,3-D formulation (InLine versus Telone EC, an EC containing 94% 1,3-D), plastic mulch type [low density polyethylene (LDPE) versus virtually impermeable film (VIF)] and drip tape configuration (one versus two drip tapes) on fumigant soil gas levels and growth of tomato were investigated. Tomato was planted after the recommended 3-week waiting period. Fumigant concentrations in soil were measured using Gastec detection tubes at 1 to 4 days after drip fumigation in all three tests. Measured fumigant soil gas concentrations were correlated with fumigant application rates in Spring 2002, but not in Fall 2002. Vegetables were visibly affected by residual fumigant levels in the soil and showed symptoms such as leaf chlorosis (cucumber, squash and pepper), leaf bronzing (tomato) and stem browning and stunting (all crops). Fumigant soil air levels were negatively and linearly correlated with different plant growth parameters, in particular plant vigor. The cucurbit crops showed an immediate response and high mortality within 1 week after planting. Surviving plants recovered well in fall. The solanaceous crops showed a more delayed response and lower mortality rates. However, phytotoxic effects with tomato and pepper were more persistent and plants did not seem to recover with time. Overall, fumigant residue levels and potential phytotoxicity were greater in spring than in fall. Greater fumigant soil concentrations were measured under VIF as compared to LDPE plastic mulch. The effect of drip-tape configuration varied with the type of plastic mulch that was used. The double-tape treatment resulted in lower fumigant levels at the bed center under LDPE mulch, and higher fumigant levels at the bed shoulder under VIF mulch. The formulation containing 94% 1,3-D resulted in higher soil fumigant levels as compared to the formulation containing 61% 1,3-D and 33% chloropicrin, especially with VIF mulch. Early plant vigor of tomato was negatively correlated with fumigant soil gas levels, and was especially poor following drip fumigation with 94% 1,3-D under VIF mulch.