Resistance to Helminthosporium leaf blight and agronomic performance of spring wheat genotypes of diverse origins

Helminthosporium leaf blight (HLB), caused by a complex of Cochliobolus sativus (Ito & Kurib.) Drechsler ex Dastur and Pyrenophora tritici-repentis Died, is a serious disease of wheat (Triticum aestivum L.) in the warm lowlands of South Asia. Wheat cultivars grown in the area are either susceptible to HLB or possess low levels of resistance to it. A replicated field study was conducted in 1999 and 2000 at two sites in Nepal to determine the level of HLB resistance and other desirable traits in 60 wheat genotypes of diverse origin. The test genotypes were planted in main strips divided into two strips one of which was sprayed four times with Tilt (a.i. propiconazole) @ 125 g of a.i. ha^–1. Four readings of HLB were recorded to calculate the area under the disease progress curve (AUDPC). Other traits under investigation included biomass yield (BY), grain yield (GY), 1000-kernel weight (TKW), harvest index (HI), days to heading (DH) and maturity (DM), plant height (PHT), and effective tiller number (ETN). Wheat genotypes differed significantly for all traits. Mean AUDPC values ranged from 45 to 1268. A few exotic genotypes were highly resistant to HLB. Losses in GY due to HLB ranged from 2 to 26%, and TKW was reduced by up to 33%. A few genotypes showed HLB tolerance, i.e., relatively smaller GY and TKW reductions despite high levels of HLB. In general, medium to late maturity and higher levels of HLB resistance and low to high GY and TKW characterized genotypes exotic to South Asia. Biplot analysis identified several genotypes that were HLB-resistant and agronomically superior. Results suggest it is possible to improve HLB resistance of local wheat cultivars based on selective breeding using this pool of germplasm.     

Farmer participatory evaluation confirms higher grain yields in spring wheat using a selection index for spot blotch resistance, maturity and kernel weight

Wheat (Triticum aestivum L.) cultivars for the warm regions of South Asia must produce high yields and possess resistance to spot blotch (Cochliobolus sativus), early maturity and high kernel weight. A study was conducted to determine the effectiveness of selecting for high grain yield based on a selection index for spot blotch resistance, maturity and kernel weight in four wheat crosses involving a susceptible cultivar and resistant genotypes. Initial selection of 40 progeny lines in each cross had been made using a selection index based on disease severity, days to heading and kernel weight as reported by Sharma and Duveiller [{Crop Sci 43 (2003) 2031}]. The five highest grain-yielding progeny lines from among the 40 lines in each cross, their parents and five popular commercial cultivars were evaluated in field trials at two sites in Nepal in the 2002 and 2003 wheat seasons. Multiple spot blotch assessments were made to determine the area under disease progress curve (AUDPC). Grain yield, thousand-kernel weight (TKW), days to heading and plant height were examined. The wheat genotypes in the farmer's field were also ranked on the basis of cultivar preference criteria by the local farmers. The 20 progeny lines always showed a higher (+11 to +125%) grain yield and heavier (+10 to +44%) kernels than their parents and a lower (−83 to −89%) AUDPC than the susceptible parent. The progeny lines showed 98–100% grain yield, 97–100% TKW and 66–78% AUDPC compared to the highest grain-yielding commercial cultivar. Based on the farmers' preference criteria for a desirable wheat genotype, the best progeny lines ranked from 3rd to 5th, whereas the two commercial cultivars ranked 1st (Gautam) and 2nd (BL 1473). Results indicated that selection was effective in combining adaptation genes present in a local cultivar with some level of tolerance to spot blotch and resistance genes from exotic genotypes, which translated into improved agronomic performance and disease resistance. The selection index and farmer participatory approach used in this study could serve as a guideline in breeding efforts targeted for high yielding genotypes for wheat-growing conditions in South Asia where spot blotch is a serious biotic constraint to yield.     

Wheat grain yield and stability assessed through regional trials in the Eastern Gangetic Plains of South Asia

Improving the level and stability of grain yield is the primary objective of wheat breeding programs in the Eastern Gangetic Plains (EGP) of South Asia. A regional wheat trial, the Eastern Gangetic Plains Yield Trial (EGPYT), was initiated by CIMMYT in collaboration with national wheat research programs in Bangladesh, Nepal, and India in 1999–2000 to identify wheat genotypes with high and stable grain yield, disease resistance, and superior agronomic traits for the EGP region. A set of 21 wheat experimental genotypes selected from a regional wheat screening nursery in South Asia, three improved widely grown cultivars (Kanchan, PBW343 and Bhrikuti), and one long-term cultivar (Sonalika) were tested at 9–11 sites in six wheat growing seasons (2000–2005) in the EGP. The 21 experimental genotypes were different in each year, whereas the four check cultivars were common. In each year, one or more of the experimental genotypes showed high and stable grain yield and acceptable maturity, plant height, and disease resistance compared to the check cultivars. Three improved cultivars have already been commercially released in the region through EGPYT and many germplasm lines have been used in the breeding programs as parents. Identification of wheat genotypes with high-grain yield in individual sites and high and stable yield across the EGP region underlines their value for regional wheat breeding programs attempting to improve grain yield and agronomic performance.     

Reduction in kernel weight as a potential indirect selection criterion for wheat grain yield under terminal heat stress

Heat is an important abiotic stress during wheat (Triticum aestivum L.) grain‐filling in South Asia. A study was undertaken to determine effectiveness of selection for reduction in 1000‐kernel weight (TKWR) under heat stress to increase grain yield. Selection was made for low and high TKWR and selected progenies were evaluated in timely and late seeded trials at two locations in Nepal in 2003. One thousand kernel weight (TKW), biomass yield, grain yield, harvest index (HI), grain‐filling duration (GFD) and area under spot blotch progress curve per day (AUDPC/day) were examined. The low and high TKWR groups did not differ significantly for TKW, biomass yield, grain yield, HI, days to heading, GFD and AUDPC/day under timely seeding. However, low TKWR lines showed higher TKW, biomass yield, grain yield, HI, and GFD and lower AUDPC/day than the lines with high TKWR under late seeding. Realized heritability estimates for TKWR ranged from 0.68 to 0.85. The findings show that selection for low TKWR could be used as an indirect selection criterion to identify high grain yielding lines under terminal heat stress.     

Combining ability analysis of resistance to Helminthosporium leaf blight in spring wheat

Wheat breeders in South Asia are attempting to develop wheat (Triticum aestivum L.) cultivars resistant to Helminthosporium leaf blight (HLB), which occurs mainly as a complex of spot blotch caused by Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, and tan spot caused by Pyrenophora tritici-repentis (Died.) Drechs. Information on the combining ability for HLB resistance in wheat cultivars of South Asia is not available. This study was undertaken to examine the resistance to HLB in nine genetically diverse wheat parents, and to evaluate their general combining ability (GCA) and specific combining ability (SCA) effects toward determining the genetic basis of disease resistance. Nine parents were crossed in a half-diallel mating design to produce 36 populations. The F₁ and F₂ progenies, and the parents were evaluated in replicated field tests at Rampur, Nepal. Multiple disease scores were recorded, and area under the disease progress curve (AUDPC) was calculated to measure disease severity over time. The combining ability analysis was performed using Griffing's Method 2, Model 1. The parents chosen showed wide variation for resistance to HLB. They and the F₁ and F₂ progenies differed significantly for AUDPC. GCA and SCA effects were significant in both generations suggesting that additive as well as non-additive genetic mechanisms were involved in the expression of resistance in these parents. Wheat genotypes 'SW89-5422', 'G 162', 'NL 781'and 'Chirya 7' had significantly negative GCA effects for AUDPC in both F₁ and F₂ generations, suggesting their prime suitability for use in wheat breeding programs to improve resistance to HLB. The estimate of narrow-sense heritability was 0.77 in both generations suggesting that selection for HLB resistance should be effective in these crosses. The results indicate a predominance of additive gene action in the inheritance of HLB resistance in spring wheat.     

The effect of spot blotch and heat stress on variation of canopy temperature depression,chlorophyll fluorescence and chlorophyll content of hexaploid wheat genotypes

Spot blotch, caused by Cochliobolus sativus (Ito and Kurib.) Drechsler ex Dastur, and heat stress are two important stresses of bread wheat (Triticum aestivum L.) causing substantial yield reduction in the warm areas of South Asia. These two stresses put pressure on at least 25 million hectares of wheat areas worldwide. This study was conducted to examine variation in physiological traits and its association with heat and spot blotch. Eleven diverse bread wheat genotypes were evaluated in replicated field trials under spot blotch epidemics and heat stress conditions in 2006 and 2007 at Rampur, Nepal. Canopy temperature depression (CTD), chlorophyll fluorescence (CF), chlorophyll content, percent disease leaf area, yield and yield components were recorded. Heat and spot blotch individually reduced CTD, CF, chlorophyll content, grain yield (GRY), and thousand kernel weight (TKW), with greater reductions recorded under combined stress. Genotypes showing lower GRY or TKW loss due to spot blotch also exhibited lower yield loss due to heat stress or combined heat and disease stress, suggesting an association between tolerance mechanisms to the stresses. The physiological traits chlorophyll content, CF and CTD showed higher correlations with GRY and TKW than with area under disease progress curve (AUDPC) suggesting their potential application in screening for heat and spot blotch tolerant genotypes. Genotypes with lower disease showed the highest values for chlorophyll content, CF and CTD. Our findings provide new information on the relationship of these physiological traits with spot blotch resistance and heat tolerance when examined in the same study. The physiological traits studied have potential application in integrative indirect selection criteria for improving spot botch and heat tolerance in wheat.     

Variation in sterility among wheat (Triticum aestivum L.) genotypes in response to boron deficiency in Nepal

Two field experiments were carried out at the Khairanitar Farm, Nepal during the winter season of 1993 to investigate whether wheat genotypes differ in their sterility response to low soil boron and whether boron added to soil can correct sterility. A nursery consisting of 41 diverse genotypes from Nepal, India, Bangladesh, Thailand, China, Pakistan and CIMMYT/Mexico were evaluated in a plot where severe sterility had been observed in previous years. The second experiment involved six genotypes of known sterility responses to boron grown with or without an application of boron at 1 kg ha^-1. Large differences were observed among genotypes in terms of number of grain set per ear (range 0.5 to 30 ) and sterility (5.5% to 97.5%). About one third of all the genotypes had <25% sterility and 16 of them suffered >75% sterility. The genotypes Fang-60, Sonalika, De Mai 6-22, BUC/FLK/MYNA/VL and HDW-234 were highly tolerant to boron deficiency with <10% sterility. In sharp contrast, genotypes BOW/BUT, SERI/THB, Glennson, SW-41, Yunmai-33 and UHU were highly susceptible and set virtually no grains in the boron deficient plots. Strong responses to boron application were observed and genotypic variations were evident. Boron at 1 kg ha^-1significantly reduced the number of late ears, increased number of grains per ear and grain yield in boron-responsive genotypes. Tolerant genotypes were not influenced by added boron. Given these striking genetic differences, progress in breeding wheat for B-deficient soils in Nepal should be worthwhile. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heritability estimates of field resistance to spot blotch in four spring wheat crosses

Spot blotch of wheat (Triticum aestivum L.), caused by Bipolaris sorokiniana (Sacc. in Sorok.) Shoem., is a major disease in South Asia. Popular commercial cultivars have low levels of resistance to spot blotch. Information on the inheritance of spot blotch resistance in wheat is lacking. Field studies were conducted in four wheat crosses, each involving a Chinese hexaploid parent with high levels of resistance and a commercial cultivar with low to intermediate levels of resistance to spot blotch. Data were recorded in the F₂, F₃ and F₄ generations to estimate heritability. Field studies were conducted in three years (1992–94) at Rampur. Nepal, involving 150 lines in each cross. The spot blotch score was recorded as the percentage necrosis and associated chlorosis of the two upper most leaf surface. In the F₂ generation three spot blotch readings on the flag leaf were taken whereas in the F₃ and F₄ generations four readings were recorded at 5-day intervals on the flag and the penultimate leaves. The highest disease score (HDS) and the area under disease progress curve (AUDPC) were analysed. Heritability (h²) estimates for spot blotch resistance were intermediate to high measured in terms of HDS (0.47 < h² < 0.67) and also AUDPC (0.58 < h² < 0.77) both in F₃ and F₄ generations in each of the four crosses. Heritability values were somewhat higher for AUDPC than HDS. There were significant negative correlations (r) of days to heading with HDS (-0.186 < r < -0.515) and AUDPC (-0.218 < r < -0.623). One-hundred kernel weight was significantly negatively correlated to AUDPC (-0.245 < r < -0.454) in all crosses in each generation. The results suggest that selection for resistance to spot blotch could be effective in the segregating populations generated from hexaploid wheat parents having different levels of resistance. Although AUDPC appeared to be a better measure to determine genetic differences for spot blotch in wheat, HDS would be adequate in screening trials for resistance to spot blotch.     

Selection of wheat genotypes for biomass allocation to improve drought tolerance and carbon sequestration into soils

The biomass allocation pattern of plants to shoots and roots is a key in the cycle of elements such as carbon, water and nutrients with, for instance, the greatest allocations to roots fostering the transfer of atmospheric carbon to soils through photosynthesis. Several studies have investigated the root to shoot ratio (R:S) biomass of existing crops but variation within a crop species constitutes an important information gap for selecting genotypes aiming for increasing soil carbon stocks for climate change mitigation and food security. The objectives of this study were to evaluate agronomic performance and quantify biomass production and allocation between roots and shoots, in response to different soil water levels to select promising genotypes for breeding. Field and greenhouse experiments were carried out using 100 genotypes including wheat and Triticale under drought‐stressed and non‐stressed conditions. The experiments were set‐up using a 10 × 10 alpha lattice design with two replications under water stress and non‐stress conditions. The following phenotypic traits were collected: number of days to heading (DTH), number of productive tillers per plant (NPT), plant height (PH), days to maturity (DTM), spike length (SL), kernels per spike (KPS), thousand kernel weight (TKW), root biomass (RB), shoot biomass (SB), root to shoot ratio (R:S) and grain yield (GY). There was significant (p < 0.05) variation for grain yield and biomass production because of genotypic variation. The highest grain yield of 247.3 g/m² was recorded in the genotype LM52 and the least was in genotype Sossognon with 30 g/m². Shoot biomass ranged from 830 g/m² (genotype Arenza) to 437 g/m² (LM57), whilst root biomass ranged between 603 g/m² for Triticale and 140 g/m² for LM15 across testing sites and water regimes. Triticale also recorded the highest R:S of 1.2, whilst the least was 0.30 for wheat genotype LM18. Overall, drought stress reduced total biomass production by 35% and R:S by 14%. Genotypic variation existed for all measured traits useful for improving drought tolerance, whilst the calculated R:S values can improve accuracy in estimating C sequestration potential of wheat. Wheat genotypes LM26, LM47, BW140, LM70, LM48, BW152, LM75, BW162, LM71 and BW141 were selected for further development based on their high total biomass production, grain yield potential and genetic diversity under drought stress.     

Ethyloxanilates as specific male gametocides for wheat (Triticum aestivum L.)

Induction of male sterility by deployment of male gametocides holds immense potential in heterosis breeding of wheat. The efficacy of a new class of male gametocide for wheat (Triticum aestivum L.) is described: ethyloxanilates, the most active example of this class being ethyl 4‐fluorooxanilate (E4FO). E4FO induces male sterility, specifically, without detectable effects on various agronomic features and female fertility. The plants sprayed once with 0.15% E4FO exhibited 100% pollen and floret sterility without causing a significant reduction in total yield. E4FO was screened on 29 genotypes of wheat at 0.15% test concentration and was observed to induce 99.76 ± 0.37% male sterility. Thirteen F₁‐hybrids of wheat were produced using the gametocide in Winter 2000–2001 and were evaluated for their agronomic performance in Winter 2001–2002. The cross combinations viz., lines WR 544 × HW 2046 and HW 2044 × WR 956 have outperformed their respective better parents by 48.17% and 23.42% in grain yield/plant and thus have potential as hybrids.     

Challenges to wheat production in South Asia

Wheat is the second major staple crop, after rice, in India and Pakistan and is also gaining similar importance in Nepal and Bangladesh. Wheat production in South Asia has increased from 15 mt in 1960s to 95.5 mt during 2004–2005. It still needs to grow at the rate of 2–2.5% annually until the middle of 21st century. However, for India, recent estimations have shown a growth requirement of about 1.1%. Although the wheat improvement programs in these countries, with the active collaboration of national agricultural research centers (NARS) and CIMMYT, has made a significant progress, it is a matter of significant concern that wheat production has stagnated for last few years. Since there is little scope for increasing land area under wheat, the major challenge will be to break the yield barrier by pragmatic genetic and developmental approaches. The most serious constraints to wheat production in this region are a host of biotic and abiotic stresses. Although India has not faced any rust epidemic in the last decade, rusts continue to occupy the place of most dangerous pathogen for the region. Among the abiotic stresses, unusual warming trends during grain filling period are causing yield declines, especially in eastern and central India. There are other challenges that are specific to the highly productive rice–wheat cropping system predominant in the Indo-Gangetic plains. The total factor productivity of this system is declining due to depletion of soil organic carbon. Addition of organic matter to soil through green manuring and crop residue recycling, balanced fertilization, integrated nutrient management, diversification of rice-wheat system are some of the possible remedial measures to improve total factor productivity. The international linkages with CIMMYT needs to be strengthened more closely for developing more productive wheat genotypes and thus, achieving wheat targets in the South Asian region.     

Improved winter wheat genotypes for Central and West Asia

High grain yield and resistance to stripe (yellow) rust are the most important traits for successful adoption of winter wheat varieties in Central and West Asia. This study was conducted to determine the stripe rust response and agronomic performance of a set of breeding lines recently developed by the International Winter Wheat Improvement Program (IWWIP). Replicated field studies were conducted in 2010 and 2011 using 38 experimental lines, one regional check (Konya) and one local check. Stripe rust scores were recorded at Karshi, Uzbekistan, and Karaj and Mashhad, Iran, in 2010. Grain yield was recorded at two sites each in Uzbekistan (Karshi and Kibray) and Iran (Karaj and Mashhad) and one site in Turkey (Eskisehir). The test lines showed variation for stripe rust severity, grain yield, 1,000-kernel weight, days to heading and plant height. Several stripe rust resistant genotypes were either higher yielding or equal to the local checks at different sites. Based on stripe rust resistance and yield performance in 2010, a set of 16 genotypes was selected and evaluated in 2011. All 16 were resistant at Almaty, Kazakhstan, and Dushanbe, Tajikistan, in 2011, whereas 9 of the 16 were resistant at Terter, Azerbaijan. The genotypes ‘TCI-02-138, ‘Solh’, ‘CMSS97M00541S’, ‘TCI -2-88(A)’ and ‘TCI-02-88(C)’ were consistently resistant to stripe across all sites in both years. Several lines showed high grain yields and superior agronomic performance across four sites in Uzbekistan and one site in Tajikistan. One genotype has been released in Uzbekistan and another in Tajikistan.     

Genetic improvement trends in agronomic performances and end-use quality characteristics among hard red winter wheat cultivars in Nebraska

Evaluation of wheat cultivars from different eras allows breeders to determine changes in agronomic and end-use quality characteristics associated with grain yield and end-use quality improvement over time. The objective of this research was to examine the trends in agronomic and end-use quality characteristics of hard red winter wheat cultivars grown in Nebraska. Thirty historically important and popular hard red winter wheat cultivars introduced or released between 1874 and 2000 were evaluated at Lincoln, Mead and North Platte, Nebraska in 2002 and 2003. An alpha lattice design with 15 incomplete blocks of two plots and three replications was used at all locations. Agronomic (days to flowering, plant height, spike length, culm length, grain yield and yield components, and grain volume weight) and end-use quality (flour yield, SDS-sedimentation value, flour protein content, and mixograph time and tolerance) traits were measured in each environment. Highly significant differences were observed among environments, genotypes and their interactions for most agronomic and end-use quality characteristics. Unlike modern cultivars, older cultivars were low yielding, and less responsive to favorable environments for grain yield and yield components. Semidwarf cultivars were more stable for plant height than traditional medium to tall cultivars. All cultivars had high grain volume weight since it is part of the grading system and highly selected for in cultivar release. Modern cultivars were less stable than older cultivars for SDS-sedimentation and mixing tolerance. However, the stability of older cultivars was attributed to their having weak mixing tolerance and reduced SDS-sedimentation values. The reduced protein content of modern cultivars was offset by increased functionality, as measured by mixograph and SDS sedimentation. In conclusion, breeders have tailored agronomic and end-use quality traits essential for hard red winter wheat production and marketing in Nebraska.     

Genotypic and temperature effects on wheat grain yield and quality in a hot irrigated environment

High temperature influences both grain yield and end‐use quality of wheat. The objectives of this study were to evaluate the performance of selected wheat genotypes under heat stress and to examine the effects of high temperatures during grain filling on grain yield and end‐use quality parameters. Fifteen bread wheat genotypes in 2000/2001 and 18 genotypes in 2002/2003 were evaluated under the optimum and late‐sowing conditions of the irrigated hot environment of the Gezira Research Farm, Wad Medani, Sudan. The genotypes comprised released varieties and elite lines from the Sudanese wheat improvement programme. Data collected included grain yield, grain weight and grain end‐use quality including protein content, protein composition, SDS sedimentation values (SDSS) and gluten strength as determined by mixograph analyses. High temperatures significantly decreased grain yield by decreasing grain weight. Although genotypes exhibited variation in magnitude of response, results indicated that high temperature during grain filling increased both soluble and insoluble protein contents, SDSS, mixograph peak height (MPH) and the descending slope at 2 min past peak (MDS). In contrast, mixograph peak time (MPT) and the curve width at 2 min past peak (MCW) were significantly decreased. Flour protein correlated positively with SDSS, MPH and MDS and negatively with MCW. MPT correlated negatively with MDS and positively with MCW. Results indicate that high temperature increased both soluble and insoluble protein contents, SDSS and MPH, and hence the gluten strength, but decreased flour mixing time and tolerance and hence the dough elasticity. Variation observed among genotypes suggests that grain end‐use quality could be improved under high temperature conditions utilizing the available variability; however, it might require evaluation under various growing conditions.     

Screening for lodging resistance in spring wheat breeding programmes

Selection for lodging resistance in Canadian hard red spring wheat under natural conditions is difficult due to the sporadic and often random nature of lodging events. We conducted field trials in Edmonton AB Canada (2000–2002) to determine if either a high seeding rate, or artificially inducing lodging (by dragging a weighted apparatus across plots at the early milk stage), would be an effective screen for determining genetic lodging resistance in wheat breeding programmes. For the 25 genotypes tested, applying artificial lodging at the experimental mean early milk stage was a suitable method to screen and identify lodging tolerant and susceptible genotypes. Tolerance to artificially induced lodging was mainly found within semi‐dwarf genotypes, and susceptibility was mainly found within Canadian bread wheat genotypes. Severe lodging resulted in yield losses as high as 40%. Lodging tolerant genotypes identified in this study are now being crossed into elite western Canadian bread wheat in an effort to increase genetic lodging resistance within Canadian breeding lines.     

High yielding spring bread wheat germplasm for global irrigated and rainfed production systems

Global wheat (Triticum aestivum L.) production must increase 2% annually until 2020 to meet future demands. Breeding wheat cultivars with increased grain yield potential, enhanced water-use efficiency, heat tolerance, end-use quality, and durable resistance to important diseases and pests can contribute to meet at least half of the desired production increases. The remaining half must come through better agronomic and soil management practices and incentive policies. Analyses of the recent International Yield Trials indicate that grain yields of the best new entries were usually 10% higher than the local checks globally, as well as within a country across sites. Variation in yield across sites within a country/region underline the role of genotype × environment (GE) interaction and provides opportunities to select for stable genotypes, which is not often done. The lack of proper analysis undermines proper utilization of germplasm with high yield potential and stability in the national wheat breeding programs. Some of the best performers in irrigated areas were amongst the best in semiarid environments, reinforcing the fact that high yield potential and drought tolerance can be improved simultaneously. The best performing lines often had genotypic base of widely adapted genotypes Kauz, Attila, Baviacora, and Pastor, with genetic contributions from other parents including synthetic wheat. We recommend within country multilocation analysis of trial performance for a crop season to identify lines suiting particular or different locations within a country. The immediate feedback on GE interaction will also help in breeding lines for countries having substantial variation across locations and years.     

从产量和品质性状的变化分析北方冬麦区小麦品种抗热性

培育抗热性强的品种对应对气候变化,保障小麦稳产性具有重要意义。选用北方冬麦区53份主栽品种和苗头品系,于2008—2009年度分别种植在北京、石家庄、衡水、安阳和泰安5点,各点设正常温度和塑料棚热胁迫处理。结果表明,千粒重可作为抗热性筛选的简易指标。农大189、CA0518和京冬8号的产量和千粒重在正常和热处理环境中均较高,抗热性好;衡观33和CA0736的产量在正常和热处理环境中均较高,但千粒重均表现中等,抗热性较好;农大211、石麦15、济麦22、农大3432和山农2149在正常环境中的产量和千粒重均较高,但在热处理环境中产量和千粒重均较低,抗热性差。53份品种按和面时间和峰值曲线面积可分为强筋、中强筋、中筋、中弱筋和弱筋5大类。热处理使所有类型材料的蛋白质含量和籽粒硬度增加,峰值带高、8min带高和8min带宽降低,并降低强筋、中强筋和中筋类型材料的和面时间与峰值曲线面积,增加中弱筋和弱筋类型材料的和面时间与峰值曲线面积。     

Effects of Early and Late Harvest on Agronomic Performance and Stability of Late Blight Resistant (R-gene Free) Potato Genotypes

Late blight is an important constraint to potato production and genotype resistance is an effective disease control mesure. Ten late blight resistant potato genotypes (R-gene free) were assessed for yield performance and stability at early (90 days) and late harvest (120 days) at two locations in Kenya during two years. Significant differences (P ≤ 0.05) in area under disease progress curves (AUDPC) were detected among potato genotypes. Resistant genotypes free of R-genes had significantly (P ≤ 0.05) higher yield at late than early harvest, perhaps due to increased tuber bulking period. The rank of genotypes for AUDPC, late blight resistance, and tuber yield varied across seasons and locations (environment). Additive main effects and multiplicative interaction (AMMI) analysis of tuber yield and late blight resistance resulted in significant (P ≤ 0.05) effects of genotypes (G) and environments (E). The proportion of genotypic variance was larger than the environmental variance and the G × E interactions. For tuber yield, the G, E, and G × E interactions accounted for 42.9, 39.6 and 17.5%; and 53.4, 29.7, and 16.9% at early and late harvests, respectively. For AUDPC, G, E, and G × E accounted for 80.2, 5.0, and 14.8%; as well as 82.3, 4.6, and 13% for early and late harvests, respectively. The resistance of potato genotypes without R-genes varied. Selective deployment of resistant genotypes can improve potato tuber yield.     

Agronomic Variability in Selected Triticum turgidum x T. tauschii Synthetic Hexaploid Wheats

Two trials were conducted at the Mexican National Institute of Agricultural Research Experiment Station at Yaqui Valley, Sonora, Mexico to investigate the nature and extent of agronomic variation in 50 synthetic hexaploid (SH) wheats (2n = 6x = 42, AABBDD) derived from Triticum turgidum (2n = 4x = 28. AABB) × T. tauschii (In = 2x = 14, DD) crosses for subsequent use in wheat improvement. Plant height, spike length, days to flowering, physiological maturity, grain yield, above-ground biomass at maturity, harvest index, yield components and test weight were determined.
Significant agronomic variation was observed among the germplasm evaluated. Outstanding SH genotypes were identified with higher grain yield, above-ground biomass at maturity, 1000-grain weight, and spikes m⁻² than the bread wheat ( Triticum aestivum L.) check cultivar Seri 82. Genotypic correlations of grain yield with other character traits show that grain m² was the most important determinant of gram yield (r = 0.993). Data on agronomic traits subjected to complete linkage cluster analysis resulted in classifying the genotypes into two distinct phenotypic groups excluding Seri 82. Groups generally corresponded to durum progenitors of the SH with significant group differences for all characters. This demonstrates use of practical numerical analysis procedures to describe agronomic variation in representative SH genotypes. Clustering by quantitativy traits may be valuable for identification of genotypes with divergent sources for breeding and agronomic purposes.     

Drought Priming at Vegetative Growth Stage Enhances Nitrogen‐Use Efficiency Under Post‐Anthesis Drought and Heat Stress in Wheat

To study the effects of early drought priming at 5th‐leaf stage on grain yield and nitrogen‐use efficiency in wheat (Triticum aestivum L.) under post‐anthesis drought and heat stress, wheat plants were first exposed to moderate drought stress (drought priming; that is, the leaf water potential reached ca. ?0.9 MP a) at the 5th‐leaf stage for 11 days, and leaf water relations and gas exchange rates, grain yield and yield components, and agronomic nitrogen‐use efficiency (ANUE ) of the primed and non‐primed plants under post‐anthesis drought and heat stress were investigated. Compared with the non‐primed plants, the drought‐primed plants possessed higher leaf water potential and chlorophyll content, and consequently a higher photosynthetic rate during post‐anthesis drought and heat stress. Drought priming also resulted in higher grain yield and ANUE in wheat under post‐anthesis drought and heat stress. Drought priming at vegetative stage improves carbon assimilation and ANUE under post‐anthesis drought and heat stress and their combination in wheat, which might be used as a field management tool to enhance stress tolerance of wheat crops to multiple abiotic stresses in a future drier and warmer climate.