Response to two cycles of divergent selection for grain yield under drought stress in four rice breeding populations

Drought is a major production constraint in rainfed rice (Oryza sativa L.). Lack of effective selection criteria is a major limitation hampering progress in breeding for drought tolerance. In an earlier report, we showed in two populations that one cycle of direct selection was effective in increasing grain yield under stress. In the present study, we retested the efficiency of direct selection for grain yield under drought stress in rice using four populations derived from crossing upland-adapted, drought-tolerant varieties (Apo, Vandana) to high-yielding, lowland-adapted, drought-susceptible varieties (IR64, IR72). Each population was subjected to two cycles of divergent selection either under drought stress in upland or under nonstress conditions in lowland conditions. Following selection, approximately 40 high-yielding lines selected under each protocol from each population, along with a set of unselected lines, were evaluated in a series of selection response trials over a range of moisture levels. Significant response to direct selection under stress was realized in 9 out of 15 combinations of populations and stress environments, and in 6 of the 7 severe stress trials. Averaging over all the populations and stress environments, the stress-selected lines had a yield advantage of 25 and 37% over nonstress-selected and random lines, respectively. In contrast to this, under nonstress, the nonstress-selected lines had an average yield advantage of only 7 and 13% over stress-selected and random lines, respectively. Direct selection in managed stress trials during dry seasons gave significant response (25% on average relative to indirect selection in nonstress conditions) under naturally occurring wet season stress. In addition, direct selection under stress in upland gave an average gain of 16 and 45% over nonstress-selected and random lines, respectively, under stress in lowland. The yield advantage of the stress-selected lines appears to result mainly from maintenance of higher harvest index. These results show that direct selection for grain yield under stress is effective and does not reduce yield potential. Overall, this is the first report in rice demonstrating that (a) selection under managed drought stress in the dry season can result in yield gains under natural stress in the wet season, and (b) that selection under upland drought stress can, at least under the conditions of the present study, result in gains under lowland drought conditions.     

Implications of genotype × input interactions in breeding superior genotypes for favorable and unfavorable rainfed upland environments

Resource-poor farmers in India cultivate upland rice as a subsistence crop in poor soil with minimum inputs, often applying little or no fertilizer and controlling weeds by hand. Consequently, upland rice yields are very low. In our study, the response to management intensification of fertilizer application at rates of 40 N ha⁻¹, 13 P ha⁻¹, and 16.7 K ha⁻¹ and two weed control treatments as compared with no fertilizer, and one hand weeding practice commonly followed by farmers in rainfed upland areas was examined with a large set of advanced breeding lines and adapted upland varieties tested over 3 years in multi-location trials. Highly significant genotype × environment interaction was observed in combined analyses across environments, leading to sub-grouping of sites into the high-yielding or favorable and low-yielding or unfavorable upland environment groups. A significant effect of management regime was observed. Averaged over 15 environments, the moderate-input treatment out-yielded the low-input treatment by nearly 65% or 0.8 t ha⁻¹ under favorable environments and by nearly 48% (0.3 t ha⁻¹) in unfavorable environments. A significant genotype effect and genotype × input management interaction for yield at favorable sites was observed. However, the same was not significant at unfavorable sites. Varietal differences were relatively small at unfavorable sites across input levels. The heritability estimates for grain yield were moderately high in both moderate- and low-input conditions in favorable environments. The genetic correlation between yields in moderate- and low-input conditions was high in both favorable and unfavorable environments. The study indicated that improved varieties performed well relative to landraces under low-input management. Improved varieties along with modestly intensified management offer an attractive option to increase the productivity of rainfed upland environments. For both favorable and unfavorable environments, indirect selection under moderate-input conditions was less efficient than direct selection for grain yield in low-input conditions, indicating upland breeding programs to adopt selection for grain yield under both moderate- and low-input conditions.     

Genetic analysis of rainfed lowland rice drought tolerance under naturally-occurring stress in eastern India: Heritability and QTL effects

Drought tolerance is an important rainfed rice breeding objective, but because the heritability (H) of yield under drought stress is thought to be low, secondary physiological traits are considered better targets for selection than yield under stress per se. This assumption has rarely been tested, and there are no reports on H for yield under drought stress from experiments repeated over seasons in rainfed lowland rice. To assess the potential for improving yield under drought stress via direct selection, and to identify associated quantitative trait loci (QTL), doubled haploid lines with a narrow range of flowering dates, derived from the population CT9993-5-10-1-M/IR62266-42-6-2, were screened under full irrigation and severe drought stress induced by draining the paddy before flowering in 2000–2002 at Raipur, India. Drought stress reduced mean yield by 80%. H was similar in stress and non-stress trials, as was the relative magnitude of the genotype and genotype × year variances. The genetic correlation between yield in stress and non-stress conditions was 0.8, indicating that about 64% of the genetic variation for yield under stress was accounted for by differences in yield potential also expressed in irrigated environments. These results indicate that direct selection for yield under drought stress can produce yield gains under stress without reducing yield potential. There was no secondary trait for which selection resulted in greater predicted response in yield under stress than direct selection for stress yield per se. A QTL was detected on chromosome 1 near sd1 that explained 32% of the genetic variation for yield under stress, but only 4% under non-stress. Its effect was consistent across years. This QTL accounted for much of the variation in drought yield not accounted for by variation in yield potential.     

Improvement of rice drought tolerance through backcross breeding: Evaluation of donors and selection in drought nurseries

A large-scale backcross breeding project has been undertaken to improve drought tolerance in rice. Over 160 donor cultivars from 25 countries have been used in this project, representing a significant proportion of the genetic variation in cultivated rice. These cultivars were evaluated in field experiments in the Philippines to assess their responses to drought in terms of plant height, heading date, and grain yield. Drought was imposed near heading stage, in experiments that were established either in lowland (anaerobic) fields or upland (aerobic) soil. Despite the poor adaptation of some cultivars to the tropics, it was possible to identify significant variation in plant response to drought treatments, and contrasting effects on flowering delay and growth. Subsequently, 325 BC₂F₂ bulk populations, developed by backcrossing many of these donors to one of three elite recurrent parents, were screened under drought in lowland or upland nurseries. Stress levels were managed to eliminate almost all seed set in recurrent parents, and those progeny that produced grain were selected as being putatively drought-tolerant. The selection intensity varied across years and in selection environments with more severe stress, higher selection intensity could be imposed. The number of plants selected within a population was not associated with the per se drought response of the donors in the direct evaluation, indicating the wide presence of cryptic genetic variation for drought tolerance in the apparently drought-susceptible cultivars. The genetic background of the recurrent parent affected the number of plants selected, as did the selection environment (upland versus lowland nurseries). These drought-selected introgression lines represent a useful genetic resource to develop improved cultivars for farmers in rainfed or water-scarce rice-growing regions, and also to improve our understanding of the genetic and molecular basis of drought tolerance in rice. Genetic analysis of the selected lines, reported elsewhere, indicated specific regions of high introgression. Yield evaluations of the selected lines are now underway across a range of drought scenarios.     

几个龙生型花生的耐旱形态性状研究

通过人工模拟干旱胁迫处理和比较其它花生类型的耐旱品种，研究几个龙生型花生在缺水条件下的形态特征及恢复生长能力，试验表明，干旱胁迫显著抑制花生地上部营养体生长，但促进主根伸长和根系干物质积累，龙生型花生耐旱性状突出，但不同材料差异较大，马山二洋和托克逊小花生是耐旱性良好的龙生型种质。     

Susceptibility of Brazilian populations of Diatraea saccharalis to Cry1Ab and response to selection for resistance

The sugarcane borer, Diatraea saccharalis (F.), is a key pest of sugarcane and other grasses, which is a current focus of research aiming to develop transgenically resistant genotypes. However, the current susceptibility of Brazilian populations of the sugarcane borer to Bt toxins is unknown. Laboratory assays were carried out to characterize the susceptibility of sugarcane borer to the Bt toxin Cry1Ab and to select a resistant strain for additional studies on Cry1Ab resistance. Susceptibility was characterized by exposing neonates of different Brazilian colonies of sugarcane borer to different concentrations in meridic diet using surface application of Cry1Ab toxin. Selection for Cry1Ab resistance was carried out by exposing neonates to Cry1Ab-expressing maize (MON 810). The resistance of the borer populations to Cry1Ab was variable with LC₅₀ and EC₅₀ values reaching about 30-fold. The larvae responded positively to Cry1Ab selection exhibiting a 55-fold increase in resistance after four generations. This suggests the suitability of using leaves containing Bt-expressing genes for selection and the existence of variability of Bt-resistance in populations of the sugarcane borer.     

Genotypic variation and selection of traits related to forage yield in tall fescue under irrigated and drought stress environments

Development of a standard evaluation protocol has been a pressing problem for the selection of drought‐resistant genotypes of tall fescue (Festuca arundinacea). This study was conducted to evaluate the association of forage yield with specific phenological and morphological traits to find a proper model for indirect selection under irrigated (normal) and drought‐stress conditions in tall fescue. A random sample of seventy‐five genotypes were clonally propagated and evaluated in normal and drought‐stress environments in the field during 2009 and 2010. Results showed that water stress had a negative effect on forage yield and most of the morphological traits measured and reduced genotypic variation for most of them. Forage yield had the highest genotypic variation, whereas days to pollination had the lowest variation. Low broad‐sense heritability estimates were obtained for dry‐matter yield, but heritability for the traits of number of stems per plant, plant height and crown diameter was moderately high. These traits were identified as the main components of forage yield. The importance of these components and their direct and indirect effects on forage yield was different in normal and drought‐stress conditions. This suggests that indirect selection for developing high‐yielding, drought‐tolerant varieties should be performed under drought‐stress conditions with a specific model.     

Heat and drought stress on durum wheat: Responses of genotypes,yield, and quality parameters

Heat and/or drought stress during cultivation are likely to affect the processing quality of durum wheat (Triticum turgidum L. ssp. durum). This work examined the effects of drought and heat stress conditions on grain yield and quality parameters of nine durum wheat varieties, grown during two years (2008–09 and 2009–10). Generally, G and E showed main effects on all the parameters whereas the effects of G × E were relatively small. More precipitation in Y09–10 may account for the large differences in parameters observed between crop cycles (Y08–09 and Y09–10). Combined results of the two crop cycles showed that flour protein content (FP) and SDS sedimentation volume (SDSS) increased under both stress conditions, but not significantly. In contrast the gluten strength-related parameters lactic acid retention capacity (LARC) and mixograph peak time (MPT) increased and decreased significantly under drought and heat stress, respectively. Drought and heat stress drastically reduced grain yield (Y) but significantly enhanced flour yellowness (FY). LARC and the swelling index of glutenin (SIG) could be alternative tests to screen for gluten strength. Genotypes and qualtiy parameters performed differently to drought and heat stress, which justifies screening durum wheat for both yield and quality traits under these two abiotic stress conditions.     

Simultaneous selection for seed and forage production in cocksfoot (Dactylis glomerata): application of drought tolerance and susceptibility indices

An experiment was conducted to estimate drought tolerance of some cocksfoot genotypes based on seed and forage yield and related indices (including tolerance index, mean productivity, geometric mean productivity, reduction percentage index, stress tolerance index and stress susceptibility index) and to identify relationships between measured traits. Twenty‐five genotypes were evaluated in the field under control and drought‐stress environments over 2 years. The results revealed a high variation for seed yield and forage yield and the measured indices under both moisture conditions. No correlation was observed between seed yield and forage yield under the control treatment, but this correlation was positively significant under the water‐stress treatment. Drought‐tolerant and susceptible genotypes were identified based on seed and forage yield performance. Genotypes 2, 4 and 7 had high seed yield, while genotypes 7 and 10 had high forage yield under both stressed and non‐stressed conditions and were identified as the most tolerant genotypes in each category. The results also revealed that genotypes 1, 2, 4, 6, 7, 8 and 24 had relatively high seed and forage yield in both control and drought‐stressed conditions. These genotypes can be used for further studies to improve both seed and forage yields concurrently.     

Characterization of phenotypic diversity,yield and response to drought stress in a collection of Rhodes grass (Chloris gayana Kunth) accessions

Information on available diversity and drought resistance among Chloris gayana accessions would offer considerable potential to select genotypes to alleviate the feed inadequacy that constrains livestock production in dry tropical areas. A collection of 62 C. gayana accessions from the genebank of the International Livestock Research Institute in Ethiopia was characterized using a set of 30 morphological, 4 phenological and 8 agronomic traits to assess diversity within the collection and to select promising accessions for use as livestock feed. In parallel, an experiment was conducted to assess the ability of these C. gayana accessions to maintain productivity under drought stress.     

两个微胚乳超高油玉米群体粒重和含油率对混合选择的选择响应

利用合成的黄粒和白粒两个微胚乳超高油玉米原始群体(C0),经过两年四轮回的混合选择改良,通过测定各轮回群体的5粒重、含油率和5粒油重三个性状,研究其选择响应.结果表明:黄、白两个群体,5粒重、含油率及5粒油重三个性状的原始群体及各轮回群体间都存在极显著差异.在第四轮混合选择(C4)后的5粒重最高,黄色群体C4y的5粒重...     

Assessing the genetic resources to improve drought tolerance in sugar beet: agronomic traits of diverse genotypes under droughted and irrigated conditions

Drought is the major cause of sugar beet (Beta vulgaris L.) yield losses in the UK and many other regions where the crop is not normally irrigated. However, drought tolerance has not been a breeding target partly because the extent of the problem was not understood, it is difficult to design effective selection screens, and because of the suspicion that few varietal differences existed. The aim of this study was to evaluate the genetic resources necessary to improve drought tolerance. Specific objectives were to assess the degree of genotypic diversity for drought tolerance, characterise genotypic differences in response to drought, and identify sources of germplasm with greater drought tolerance than current commercial varieties. Over 3 years, 46 beet genotypes representing diverse genetic backgrounds were tested in the field under large polythene covers to impose a drought beginning approximately 40 days after emergence until harvest. Sugar, root and total dry matter yields were measured under drought and irrigated conditions. The percentage green crop cover was measured at regular intervals and used in the calculation of radiation use efficiencies for each genotype. Drought tolerance index (DTI) was computed as the fraction of irrigated yield maintained under drought, normalised by the mean yield across all genotypes in the trial. Seven genotypes were tested in all years, and the data on these were used to calculate yield stability statistics and to estimate broad-sense heritability. There were more than two-fold differences in droughted and irrigated yields between genotypes, and nearly a two-fold difference in DTI. According to an index that combines yield potential and drought tolerance, some genotypes performed better than the three locally adapted commercial varieties included in the test. There were significant effects for genotype, treatment and G×E interactions for yield components and radiation use efficiency. There were also significant genotype differences in harvest index but few significant G×E interactions. Droughted and irrigated yields were positively associated, but there was no close relation between yield potential and DTI. The seven genotypes common to all years differed in yield stability and in sensitivity to water availability. Thus, the genetic resources exist for germplasm improvement. Both yield potential and DTI (which may ensure better yield stability) should be considered simultaneously as breeding targets for drought-prone areas.     

Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut (Arachis hypogaea L.)

More rapid progress in breeding peanut for reduced aflatoxin contamination should be achievable with a better understanding of the inheritance of, aflatoxin trait and physiological traits that are associated with reduced contamination. The objectives of this study were to estimate the heritability of aflatoxin traits and genotypic (r_G) and phenotypic (r_P) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F_4:6 and F_4:7 generations were generated from four crosses, and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008. Data were recorded for biomass (BIO), pod yield (PY), drought tolerance traits [harvest index (HI), drought tolerance index (DTI) of BIO and PY, specific leaf area (SLA), and SPAD chlorophyll meter reading (SCMR)], and aflatoxin traits [seed infection and aflatoxin contamination]. Heritabilities of A. flavus infection and aflatoxin contamination in this study were low to moderate. The heritabilities for seed infection and aflatoxin contamination ranged from 0.48 to 0.58 and 0.24 to 0.68, respectively. Significant correlations between aflatoxin traits and DTI (PY), DTI (BIO), HI, biomass and pod yield under terminal drought conditions were found (r_P = −0.25** to 0.32**, r_G = −0.57** to 0.53**). Strong correlations between SLA and SCMR with A. flavus infection and aflatoxin contamination were also found. Positive correlations between SLA at 80, 90, and 100 DAP and aflatoxin traits were significant (r_P = 0.13** to 0.46**, r_G = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (r_P = −0.10** to −0.40**, r_G = −0.11** to −0.66**). These results indicated that physiological-based selection approaches using SLA and SCMR might be effective for improving aflatoxin resistance in peanut.     

Variation in root system architecture and drought response in rice (Oryza sativa): Phenotyping of the OryzaSNP panel in rainfed lowland fields

Root growth at soil depths below 30 cm may provide access to critical soil water reserves during drought in rainfed lowland rice. In this study, the OryzaSNP panel, a set of 20 lines representing genetic diversity in rice used for the discovery of DNA sequence polymorphisms, was evaluated for root characteristics in the field over three seasons varying in drought severity. Root length density (RLD) at a depth of 30–45 cm varied up to 74–92% among genotypes under drought stress (2008–2009 dry seasons), ranging from 0.024 to 0.23 cm cm⁻³ in 2008 and from 0.19 to 0.81 cm cm⁻³ in 2009. Real-time monitoring of soil moisture profiles revealed significant differences among genotypes, and these differences were correlated with RLD at those soil depths. Among the lines evaluated, the Aus isozyme group, particularly the genotype Dular, showed greater drought resistance associated with deep root growth and the highest drought response index (less reduction in yield by drought stress). Since the set of genotypes used in this study has been completely sequenced for SNP markers, the phenotypic information on root growth and drought avoidance responses presented here could be used in initial analysis of the genetic basis of dehydration avoidance traits and in facilitating improvement in drought resistance in rice.     

高产抗病优质芝麻新品种中芝12的选育

中芝12是中国农业科学院油料作物研究所以国外引进的芝麻品种"CLSU-9"作母本、以本地品种"宜阳白"作父本杂交,经多代定向选择育成的芝麻新品种,具有高产稳产、抗(耐)茎点枯病和枯萎病强、品质优、适应性广等特性.2001-2002年湖北省芝麻区试中平均产量1 213.2kg/hm2,比对照鄂芝2号增产14.32%.茎点枯病和枯萎病病情指数分别为6.56和1.62,比对照分别低35.9%和17.8%.种子含油量56.09%,蛋白质含量20.11%.2003年通过湖北省农作物品种审定委员会审定.     

Influence of the soil physical environment on rice (Oryza sativa L.) response to drought stress and its implications for drought research

Plant performance under drought stress is not solely defined by an inadequate water supply but by an interaction among many factors, including climatic, edaphic, and biological factors. An important interacting factor affecting root growth, and therefore the ability of a plant to access and take up water, is the soil physical environment. Soil penetration resistance can restrict, or even halt, root system growth. For rice, a soil penetration resistance of 1.4 MPa is sufficient to inhibit root system expansion. This review describes the effects of the soil physical environment on root growth and its interaction with drought stress. A large variation in soil penetration resistance exists among rainfed rice-growing areas of South and Southeast Asia and within experimental stations used for managed-drought field phenotyping. This variability may influence genotypic performance across experimental sites/countries and the response of crop genotypes to drought stress. A case study is presented in which differences in the soil physical environment may partially elucidate differences in experimental results between two field studies conducted at different locations. These results highlight the need for increased knowledge of environmental interactions to allow the outputs of genomics to increase drought tolerance at the field level.     

Effect of tolerance to Septoria tritici blotch on grain yield,yield components and grain quality in Argentinean wheat cultivars

Septoria tritici blotch (STB) caused by Zymoseptoria tritici (Mycosphaerella graminicola) is a major disease of wheat worldwide due to significant losses in grain yield and quality. Disease tolerance is the ability to maintain yield performance in the presence of disease symptoms. Therefore, it could be a useful tool in the management of the disease. Although it is known, that there is disease tolerance to STB in some wheat cultivars, this aspect has not been studied among Argentinean cultivars. The aims of this study were to evaluate genotypic differences in tolerance to STB among Argentinean cultivars, considering the relationship between the area under disease progress curve or the green leaf area or the non-green leaf area duration with the grain yield. In addition the effect of the disease on yield, yield components, test weight, grain protein concentration, wet and dry gluten concentration and the influence of tolerance on these traits was investigated. Field experiments were carried out with ten cultivars in a split-split-plot design during 2010 and 2011. Inoculation treatments were the main plots and cultivars, the subplots. STB significantly reduced grain yield, their components, test weight and increase grain protein and gluten concentration. Cultivar Baguette 10 showed major tolerance to STB, indicated by a consistent low regression slope between the green area duration and yield, while Klein Chaja was non-tolerant due to a high regression slope. However, many cultivars such as Buck Brasil, Buck 75 Aniversario, Klein Escorpion and Klein Flecha had considerably similar regression slopes to Baguette 10, provided good levels of tolerance. Other cultivars presented no significant differences. The correlation coefficient between tolerance and grain yield potential was not significant, suggesting that tolerant high-yielding cultivars can be obtained. No relationship was found between quality group or tolerance with the increase in protein and gluten concentration due to STB either.     

Yield, water use efficiency and nitrogen uptake in potato: influence of drought stress

Summary A lysimeter experiment was performed to study the optimal allocation of limited water supply in potatoes. Irrigation regimes equal to 40, 60 and 80% of maximum evapotranspiration (ET) were evenly applied over the crop cycle. Other treatments involved withholding 80 mm of irrigation, based on ET, beginning at each of three designated growth stages (tuber initiation, early and late tuber growth). An irrigated control treatment, restoring the entire ET, was included for comparison. Continuous drought stress reduced photosynthesis as irrigation volumes were reduced. Plant biomass and tuber yield decreased almost proportionally to water consumption, so that WUE was roughly constant. N uptake was highest in the control and in 80% ET treatment. Withholding water during tuberisation severely hindered plant physiological processes and penalized tuber yield. Reductions in photosynthesis, total biomass and yield were the greatest when drought was imposed during tuber initiation. The earliest stress resulted in the lowest WUE and N uptake. A new crop water stress index (SI) was proposed, which combines atmospheric demand for water and canopy temperature.     

Preference for diverse pastures by sheep in response to intraruminal administrations of tannins,saponins and alkaloids

Plant secondary compounds (PSC) are increasingly recognized as important in animal health, welfare and nutrition, yet little is known about possible complementarities among forages that contain PSC. This study explored how sheep modify their foraging behaviour in pastures containing four forages with different PSC when challenged with intraruminal administration of a single PSC. Six pairs of lambs received a dose of a single PSC in three successive periods (1 – Condensed tannins, 2 – Saponins, and 3 – Ergotamine) of 5 d each. Six other pairs of lambs received just the vehicle. After the early‐morning dosing, lambs were allowed to graze a choice of: 1 –Lotus corniculatus [birdsfoot trefoil (BFT)], 2 –Medicago sativa [alfalfa (AA)], 3 –Festuca arundinacea [endophyte‐infected tall fescue (TF)], high in tannins, saponins and alkaloids, respectively, and 4 –Dactylis glomerata [orchard grass (OG)]. The foraging behaviour of lambs was recorded at 1‐min intervals (scans). Lambs dosed with tannins had more scans than Controls on BFT (P = 0·002) and TF (P = 0·004). Lambs dosed with saponins had more scans than Controls on TF (P = 0·01), and animals treated with ergotamine had more scans than Controls on BFT (P = 0·03). Lambs showed the lowest proportion of scans on AA after a dose of saponin (P ≤ 0·09) and on TF after a dose of ergotamine (P ≤ 0·009). Thus, lambs minimized the negative impacts of PSC through changes in their foraging behaviour by avoiding over‐ingesting any one PSC and by selectively increasing the preference for complementary PSC‐containing forages.