Analysis on genetic contribution of agronomic traits to total sugar in flue-cured tobacco (Nicotiana tabacum L.)

To uncover the genetic contributions of agronomic traits to content of total sugar (TS) and find indicator traits for indirect selection on TS in the flue-cured tobacco (Nicotiana tobacum L.), multivariable conditional analysis was conducted based on a genetic model containing additive–dominance and their interactions with environments. Fourteen cultivars (or breeding lines) and derived 41 F₁ crosses were grown at four locations in Yunnan province, China. Significant phenotypic contribution to TS was detected for six agronomic traits, plant height (PH), girth of stem (GS), internode length (INL), number of leaves (NL), length of middle leaves (LML) and width of middle leaves (WML). There was large contribution of additive effects due to each of the five agronomic traits (PH, GS, INL, LML and WML). The contribution ratio of dominance effect was high due to PH. By serving as high contributor of additive effects to TS and having high ratios of additive variance to phenotypic variance, INL and PH could be used as indicative agronomic traits for selecting breeding lines with suitable TS. Among the six agronomic traits, PH had the highest contribution to dominance effects of TS for most F₁ crosses, and could be used for selecting the crosses with suitable TS.     

Selection before backcross during exotic germplasm introgression

Introgression of genes from exotic germplasm into breeding populations can broaden the genetic base of crop improvement. Only a very small percentage of genetic variability has been used in crop breeding programs. Traditionally, F₁ plants are used to backcross to the adapted lines or populations. An alternative approach is to backcross the F₂ individuals selected for agronomic acceptability. Our objective was to determine whether selection before backcross would lead to more progenies with both high yield and acceptable levels of agronomic performance than direct backcross without selection. To test the feasibility of the proposed approach, we conducted parallel experiments in which two exotic sorghum accessions were crossed to two adapted sorghum parents and further backcrossing was conducted with either F₁ or selected F₂ plants. Fifty random S₁ families were evaluated in three test environments. Although selection before backcross resulted in a higher frequency of families with maturity equal to or earlier than those of the adapted parents, no consistent changes in grain yield and plant height were observed between populations with and without selection. Similar results were found with either an inbred or a population as the recurrent parents. Given these findings and the extra generation required, we do not recommend selection before backcross in the process of introgression of exotic germplasm.     

利用CIMMYT资源创制小麦抗病及农艺新种质的研究

为利用CIMMYT资源创制小麦抗病、农艺性状优良的新材料,以CIMMYT新培育的RL6077与西农979、周麦27等骨干品种进行冬春性杂交和(或)回交,构建RIL群体和有限回交群体;以CIMMYT材料Wheatear与豫农982进行冬春性杂交构建F2:7RIL群体。应用特异性分子标记对这些群体材料进行分子检测,同时进行田间抗病性鉴定和农艺性状选择。结果表明,RL6077后代群体的众多性状都介于两个亲本之间,很好地遗传了双亲的农艺特征;其RIL群体中更易检测到抗病基因,回交群体后代更易选出农艺性状优良的品系,可根据育种目标选用合适的群体;本研究选育出冬性、农艺性状优良且具有抗病基因(抗Ug99)的储备性新品系6份。Wheatear/豫农982的F2:7RIL群体中,1BL/1RS易位系的千粒重和叶宽显著高于非易位系;7DL·7Ag易位对穗下节长和穗粒数具有正向作用;双易位系则综合了上述特性;经田间抗病性鉴定,易位系具有良好的综合抗病性;从此群体中选育出冬性、双易位且农艺性状优良的新品系4份。     

Molecular approaches unravel the mechanism of acid soil tolerance in plants

Acid soil is a worldwide problem to plant production. Acid toxicity is mainly caused by a lack of essential nutrients in the soil and excessive toxic metals in the plant root zone. Of the toxic metals, aluminum(Al) is the most prevalent and most toxic. Plant species have evolved to variable levels of tolerance to aluminum enabling breeding of high Al-tolerant cultivars.Physiological and molecular approaches have revealed some mechanisms of Al toxicity in higher plants. Mechanisms of plant tolerance to Al stress include: 1) exclusion of Al from the root tips, and 2) absorbance, but tolerance of Al in root cells. Organic acid exudation to chelate Al is a feature shared by many higher plants. The future challenge for Al tolerance studies is the identification of novel tolerance mechanisms and the combination of different mechanisms to achieve higher tolerance. Molecular approaches have led to significant progress in explaining mechanisms and detection of genes responsible for Al tolerance.Gene-specific molecular markers offer better options for marker-assisted selection in breeding programs than linked marker strategies. This paper mainly focuses on recent progress in the use of molecular approaches in Al tolerance research.     

Selection indices for improving selection efficiency in Indian mustard

In Indian mustard (Brassica juncea L. Czern & Coss), a major oilseed brassica crop, oil yield is the ultimate trait of economic value, which is determined by seed yield (SY) and oil content (OC). SY, the end product of many complex biological processes, is influenced by many traits, such as plant height (PH), branch number, siliqua number, seed weight, seed size and pod length. It is difficult to accurately select for high-yielding genotypes based exclusively on SY, neglecting other yield-determining traits in commercial breeding programs. Therefore, it is desirable for breeders to simultaneously improve several traits of economic importance, most of which are quantitative in nature. The purpose of the present study was to develop selection indices for simultaneous selection of multiple quantitative traits to enhance selection efficiency of the mustard breeding program of Punjab Agricultural University (PAU) located in Abohar, Punjab. A set of 487 diverse mustard genotypes, comprising germplasm accessions of Indian and European origin, advanced breeding lines, landraces, and cultivars, was evaluated using an alpha lattice design for 2 years (2015–16 and 2016–17) at the Regional Research Station of PAU, Abohar, District Fazilka (the major mustard-growing region of the Punjab state). Data on PH, main shoot length (MSL), number of primary branches (NPB), number of secondary branches (NSB), number of siliquae on main shoot (NSMS), siliqua length (SL), number of seeds per pod (NSP), 1000-seed weight (TSW), SY on a plot basis and OC were recorded. To compute selection indices, economic weights, as determined via path coefficient analysis, were assigned to major yield-determining traits. Out of eight recorded agronomic traits, four traits, viz., NSMS, TSW, NSB and NPB, had larger direct effects on SY than other traits, and hence were assigned relative economic weights of 0.60, 0.20, 0.12 and 0.08, respectively. Selection indices were computed using different combinations of traits via Kang_SASPath computer program. When seven traits were used in a selection index (PH, NPB, NSB, NSMS, SY, TSW and MSL; or PH, NPB, NSB, NSMS, SY, TSW and OC), expected genetic advance (GA)at 5% selection intensity was about the same (9.55; selection efficiency or SE = 163% compared with selection based on SY alone).The GA was 9.46 (SE = 161%)for five traits, viz., NPB, NSB, NSMS, SY and TSW; and 9.30 (SE = 159%)for four traits, viz., NPB, NSB, NSMS, and TSW. These GAs were compared with the GA for SY only, which was 5.90 (benchmark; SE = 100%). We concluded that simultaneous selection based on multiple traits was always more efficient than selection based on SY alone. As there was only a small difference between the GA based on four traits (SE = 161%) and GA based on seven traits (SE = 163%), we suggest that mustard breeders use the parsimonious combination of four traits, viz., NPB, NSB, NSMS, and SY, to enhance SY and, consequently, oil yield in mustard.     

Identification and validation of QTLs for cold tolerance at the booting stage and other agronomic traits in a rice cross of a Japanese tolerant variety,Hananomai, and a NERICA parent,WAB56-104

In Africa, cold temperatures occur in the highlands of East and Southern Africa and in some areas of the Sahel region of West Africa leading to substantial rice yield losses. Cold tolerance (CT) at booting stage on basis of spikelet fertility after cold water irrigation was evaluated using F₂ population derived from a cross between temperate japonica, Hananomai, and tropical japonica, WAB56-104. Two Quantitative trait loci (QTLs) for CT were detected on chromosome 8 and 10 with enhanced effects on the trait coming from Hananomai and WAB56-104 allele, respectively. The QTLs explained 30% and 33% of phenotypic variation in spikelet fertility, respectively. CT was negatively correlated with panicle number (r = ?0.35, p < 0.01) and positively correlated with panicle weight (r = 0.61, p < 0.001). Selected BC₁F₄ and BC₁F₅ genotypes having homozygous alleles for both CT QTLs exhibited higher spikelet fertility under cold stress. The identified QTLs will be useful in the development of cold-tolerant varieties for production in high altitude areas through marker-assisted selection.     

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.     

Enhancing Salt Tolerance in Crops Through Molecular Breeding: A New Strategy

SUMMARY

Salinity limits crop production in many rainfed ecosystems and is an increasing problem in irrigated areas. Developing and developed countries alike need more efficient methods of enhancing salt tolerance in crops. The traditional breeding approach consists of (i) screening germplasm collections for donors of salt tolerance, (ii) crossing a donor with an elite line and advancing the F₁ hybrid to about the F₇ or F₈ generation while selecting for elite traits, and concurrently (iii) selecting for salt tolerance starting at about the F₄ generation. The low efficiency of this pedigree approach is due principally to the difficulty of recovering elite genotypes with salt tolerance traits, the genetic complexity of salt tolerance, and the strength of genotype × environment interactions (GEI). Advances in genomics are making possible an alternative approach in which a pre-breeding phase is used to pyramid several known genes and finely mapped major QTLs for complementary aspects of salt tolerance. The known genes can include transgenes modified by deliberate mutation or promoter switching. DNA-based selection protocols that are used to pyramid these genes are again employed during the breeding phase to transfer the entire set of genes for salt tolerance into any elite line by backcrossing. Breeding efficiency is increased because (i) elite traits are more easily recovered by backcrossing than by the pedigree approach, (ii) the genetic complexity of salt tolerance is reduced to a small set of well-defined genes and loci of large effect, (iii) the confounding effects of GEI are eliminated from the breeding phase, and (iv) the investment in gene discovery and QTL mapping can be recouped by transferring the same set of genes to a range of recipient lines that require salt tolerance. Efficiency will increase over time as more genes are added to the gene set and as QTL are replaced by the corresponding gene. Here we summarize the scientific advances underlying this new strategy, which should be applicable to other complex traits such as drought tolerance, durable resistance to pests and diseases, yield potential and product quality.     

Analysis of cold tolerance in sorghum under controlled environment conditions

Grain sorghum (Sorghum bicolor (L.) Moench) originated in the semi-arid tropics and is generally sensitive to low-temperature stress. Early planting and use of minimum tillage necessitate the development of sorghum hybrids with early season cold tolerance. Genetic variability for cold tolerance exists in sorghum and has been detected by early planting under field conditions and by analysis of seeds and plants under growth chamber conditions. There is limited information on the efficiency of evaluating cold tolerance under growth chamber conditions and the relationship with field performance. The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to exam different components of cold tolerance and their relationships, and to evaluate the consistency of lab test results with data from field tests. Thirty commercial hybrid seed lots were evaluated by growing the entries under 15/10, 13/10, 11/8, and 25/20 °C day/night temperature in a 13/11 h cycle in a growth chamber. Traits measured included emergence percentage, emergence index, shoot and root dry weight, seedling height, and vigor score. Significant genotypic differences were detected for all traits. Correlations among the traits were significant and favorable, which confirmed that simultaneous improvement of these traits should be possible. The same seed lots were also evaluated in a soil-free plate-based assay, in which percent germination, and shoot and root elongation of the seed lots grown in dark at 15 °C were measured. Results from both laboratory tests, soil-based and plate-based, were correlated with data collected in a field study, which was conducted to evaluate cold tolerance of commercial sorghum hybrids at Manhattan, Hesston, Bellville, and Garden City, KS in 1998 and 1999. Single-trait correlations between lab and field studies were significant. Differentiation based on rank-summation index of common traits, rank-summation index correlations and the overlap of best entries, further provided strong support of the efficiency of predicting and identifying elite hybrids using growth chamber assays.     

分子标记辅助选择下的玉米回交群体农艺性状分析

以综3为受体亲本、衡白522为供体亲本,通过3代回交,利用SSR标记对BC3F1群体背景进行检测,并进行群体植株重要农艺性状的分析。结果表明,群体背景回复率在94.40%以上,平均回复率为97.75%,最高回复率为100%,远远高于经典遗传学背景回复率。农艺性状分析结果显示,背景回复率并未达到分子标记结果。分子标记辅助选择是提高育种选择效果加速育种进程的有效途径之一,针对数量性状控制的农艺性状的选择还需要进一步研究。     

Characterization of sorghum genotypes for traits related to drought tolerance

Grain sorghum (Sorghum bicolor L. Moench) is a genetically diverse cereal crop grown in many semiarid regions of the world. Improving drought tolerance in sorghum is of prime importance. An association panel of about 300 sorghum genotypes from different races, representative of sorghum globally, was assembled for genetic studies. The objectives of this research were to (i) quantify the performance of the association panel under field conditions in Kansas, (ii) characterize the association panel for phenological, physiological and yield traits that might be associated with tolerance to limited moisture (drought), and (iii) identify genotypes with higher yield potential and stability under different environments that may be used in the sorghum breeding program. Results show large diversity for physiological and yield traits such as chlorophyll content, leaf temperature, grain numbers and grain weight per panicle, harvest index and yield. Significant differences were found for plant height, grain weight and numbers per panicle, harvest index, and grain yield among and within races. The US elite lines had the highest number of grains and grain weight per panicle while the guinea and bicolor races recorded the lowest. Harvest index and yield was highest for the US elite lines and the caudatum genotypes. Overall, there was a negative correlation between plant height and grain weight, grain numbers and yield. Harvest index and grain numbers were negatively affected by moisture limitation for all the races. Among the races, the caudatum genotypes were more stable in grain yield across the different environments. Overall, there was a wide variability within the association panel for physiological and yield traits that may prove to be useful for improving drought tolerance in sorghum.     

小麦抗病基因Lr68和Sr2/Yr30的遗传特性分析

为深入了解小麦抗病基因的遗传规律,以亲缘关系较远的小麦品种西农979和RL6077为亲本,构建其BC1F1和F2群体,用特异性标记csGS和WMS533分别对抗叶锈病基因Lr68、抗秆锈病和条锈病基因Sr2/Yr30进行检测,同时进行农艺性状分析。结果表明,后代群体抗病基因分布广泛,F2群体抗病基因传递率(65.41%、74.53%、48.91%)较BC1F1(44.27%、55.11%、23.66%)高,Lr68基因在两群体中的传递频率均比理论值低,不符合一对显性基因的遗传规律,Sr2/Yr30基因在BC1F1中的传递率比理论值高,在F2群体中正常,且后代群体中Sr2/Yr30基因的分布较广。后代群体在有效分蘖数、株高、穗粒数、千粒重等农艺性状上与西农979无显著差异,有效小穗数与RL6077一致,茎部指标处于两亲本之间。总体来看,后代群体保留了西农979分蘖力较强、成穗率较高、穗型中等偏大、产量稳定等优良性状,且在分蘖数、成穗率、穗粒数上还有进一步提升的空间。     

Uptake and use efficiency of N, P, K, Ca and Al by Al-sensitive and Al-tolerant cultivars of wheat under a wide range of soil Al concentrations

The impacts of acidic soils and Al toxicity on wheat nutrient economy have been scarcely researched under field conditions even though these soils are widely spread in wheat production areas around the world. The main objective of this study was to quantitatively evaluate the element (N, P, K, Ca and Al) economy of an Al-sensitive and an Al-tolerant wheat cultivar growing under different soil Al concentrations at field conditions. To reach this objective, two field experiments were conducted in an Andisol in Valdivia (39°47′18″S, 73°14′05″W), Chile. Treatments were a factorial arrangement of: (i) two spring wheat cultivars (Al-sensitive, Domo.INIA and Al-tolerant, Dalcahue.INIA) and (ii) five exchangeable Al levels (0-2.7 cmol₍₊₎ kg⁻¹) with three replicates. At harvest, plant biomass was sampled and divided into 5 organ categories: ears, grains, blade leaves, stems plus sheath leaves and roots. The element content (N, P, K, Ca and Al) in each organ was measured to quantify element uptake and concentration, nutrient uptake efficiency (UPE) and nutrient utilization efficiency (UTE). Element uptake (N, P, K, Ca, and Al) was negatively affected by the increased soil Al concentration in above-ground and root biomass in both cultivars (R² = 0.61-0.98, p < 0.01), although clear differences were found between cultivars. On the contrary, the impact of soil exchangeable Al on the plant element concentration was minor, showing weak associations with soil Al levels. However, the Al concentration in above-ground tissues of the Al-sensitive cultivar was an exception because it increased exponentially with the Al soil concentration (R² = 0.96-0.99, p < 0.001). Nutrient uptake efficiencies, UPEs (N, P, K and Ca), were negatively affected by soil Al concentrations and were well described by linear equations in both cultivars (R² = 0.58-0.98, p < 0.05), with notable differences between them. Both nutrient uptake (capture) and UPE were the traits that best explained above-ground biomass production (R² = 0.82-0.99, p < 0.001, n = 20). Nutrient utilization efficiency, UTEs (N, P, K and Ca) responded more conservatively to the soil Al concentration, except for the Al sensitive cultivar under very high soil Al levels.     

Participatory variety development for sorghum in Burkina Faso: Farmers’ selection and farmers’ criteria

Sorghum (Sorghum bicolor (L.) Moench) is the staple crop of Burkina Faso in West Africa where guinea race landraces are grown in low-input cropping systems. National and international breeding programs have had little success in disseminating modern varieties based on high yield potential caudatum or kafir race breeding materials, mostly introduced from other countries. It has been argued that the breeding objectives were not sufficiently oriented towards the farmers’ needs and preferences, and that they did not target the prevailing growing conditions of Burkina Faso. The objectives of the present article are (i) to identify and examine farmers’ selection criteria for sorghum varieties in the Centre-West of Burkina Faso, (ii) to compare these criteria with the breeder's agronomic observations and standard practices, and (iii) to show how the criteria of both farmers and breeders can be effectively integrated into the early stages of a pedigree breeding program. These objectives take into consideration gender differentiation, consistency of selection criteria and the interrelationship of measured quantitative traits, as well as the impact of these traits and criteria on the final selection. The present paper is based on a pedigree breeding program that was carried out over three years (2001–2003) in two villages of Burkina Faso. Options for integrating farmers’ selection expertise with that of the breeders’ were examined. Participatory selection was initiated with 53 F3/F4 progenies in field trials managed by farmers using rating and voting exercises. The breeders measured and analysed the agronomic data while the farmers evaluated a large number of progenies by means of their three most important selection criteria and a general appreciation. Farmers’ initial choices remained consistent in the selection exercises (voting) performed in subsequent years. The farmers’ methods for defining traits turned out to be more multivariate than the breeders’ formal understanding of these same traits. This was especially so for the criteria of grain quality, earliness, and productivity for which the farmers’ definition encompasses factors such as flour yield and stability across environments. However, rating results between farmer groups were variable. A disagreement between female and male ratings was especially found for the grain quality traits. The results clearly show that farmers can effectively select for traits on the basis of progeny and single plants while pursuing specific agronomic aims such as adaption. Subsequent yield improvement schemes will thus be more efficient in terms of selection intensity related to grain yield. The study is showing the way for breeders to adjust their selection criteria to suit the basic needs of small-scale farmer in semi-arid regions of sub-Saharan Africa.     

不同基因型油菜耐铝性及其根系形态对铝胁迫的响应

本研究旨在为酸性土壤地区筛选耐铝毒的甘蓝型油菜,探讨不同基因型油菜苗期生长发育指标和生理指标的耐铝特性,分析铝胁迫对根系形态的影响。以81个油菜品种为材料,通过水培试验,设置铝浓度（AlCl3）0、100 μmol·L-1两个处理,对根系形态、株型、生物量、生理特性等13指标的耐铝系数进行相关分析、主成分分析和聚类分析,采用隶属函数法综合评价不同基因型油菜的耐铝相关指标,并分析不同耐铝类型的品种根系形态差异。结果表明,铝胁迫对不同基因型油菜苗期各单项指标有不同程度的影响,综合应用主成分分析、聚类分析和隶属函数法筛选出耐铝性较强的品种6个,耐铝性中等的品种65个,耐铝性弱的品种10个。不同直径范围根系对铝胁迫的响应不同,铝胁迫下,D1类根系（直径0.0～0.5 mm）的长度、表面积、体积、根尖数降幅最大,D3类根系（直径>2.0mm）各指标降幅最小,且铝敏感型品种不同类别的根系指标受铝胁迫的抑制程度大于耐铝型品种,其D1、D2（直径0.5～2.0 mm）、D3类根系的长度、表面积、体积、根尖数均少于耐铝型品种。因此,以综合指标对油菜耐铝性进行筛选与评价更为客观;耐铝型品种不同直径范围的根系受铝毒害的影响较轻,通过改变根系形态适应铝胁迫的能力更强,其根系拥有更多细根可能是耐性品种抗铝毒的一种作用机制。     

甜高粱主要农艺性状的主成分分析

对国内外194份甜高粱品种进行了10个主要农艺性状调查。采用主成分分析,发现穗重、生育期、生物产量、穗长、茎粗、分蘖及含糖量等7个因子为农艺性状的主成分。在甜高粱育种中应加强生物产量选择,适当考虑含糖量及生育期,但穗重、分蘖和茎粗不宜过高,并且穗长越短越好。研究结果将为甜高粱的品种改良和创新提供理论依据。     

Inheritance of tolerance ofGlobodera pallida and the relationship between tolerance and resistance toG. pallida in potatoes

Summary The tolerance of and resistance toGlobodera pallida of two potato progenies which segregated for these characteristics were assessed in pots in the glasshouse. The level of tolerance varied widely between genotypes within the progenies, with several genotypes being significantly more tolerant than the intolerant parent. The levels of resistance and tolerance in the progenies were not significantly correlated. No indications were obtained that the ranking of genotypes for tolerance is influenced by the density ofG. pallida in the soil. The results confirm that selection for tolerance in aG. pallida resistance breeding programme is useful and feasible.     

Effects of cytoplasm,male and female parents on biomass productivity in sorghum (Sorghum bicolor L. Moench)

Production of renewable fuel requires biomass sources. To meet this need, energy sorghum was identified as a potential biomass source. Hybrid sorghum development involves the use of cytoplasmic male sterility (CMS) and since there are multiple CMS systems, it is important to determine if any of the CMS systems has an effect on agronomic performance and biomass composition. Energy sorghum hybrids were produced using four seed and four pollinator lines, resulting in 16 hybrid genotypes in three different cytoplasms (A1, A2, and A3). These hybrids were evaluated in three environments across 2 years for agronomic and biomass composition traits. For most traits, differences among hybrids and environments accounted for most of the variation, cytoplasm did not in any trait. These results indicated that different CMS systems can be used for energy sorghum hybrids without affecting yield or composition.     

A field screening technique for evaluating rice germplasm for drought tolerance during the vegetative stage

A rapid method of testing direct-seeded rainfed rices (Oryza sativa L.) for drought reaction, concurrently with, but separately from, evaluation for agronomic traits and reaction to various stresses, is needed for early identification of desirable genotypes. Thus, a technique which quantifies soil moisture stress for screening thousands of cultivars and breeding lines for drought tolerance during the vegetative stage was developed. Seeds were drilled on dry granular clay soil (Andaqueptic Haplaquoll) in the field, then sprinkler-irrigated every 4 days for 37 days. As the soil dried, each entry was visually scored for drought reaction at 0.1–0.2, 0.4–0.5 and 0.8–1.0 MPa soil moisture tension (smt) at 20-cm soil depth. Entries were visually scored for drought recovery 10 days after the field was reirrigated. A total of 38 691 rices was tested in the dry seasons from 1978 to 1985. The 8-year screening test showed reproducibility of results in the field as indicated by the consistent scores of drought-tolerant and susceptible control cultivars within and across years. Ten germplasm accessions repeatedly performed similar to, or better than, the drought-tolerant control. There were ten outstanding drought-tolerant breeding lines, six of which were progenies of moderately tolerant Nam Sagui 19 from Thailand. The 20 outstanding selections likewise had consistent drought-tolerant scores across years, irrespective of duration of stress, which ranged from 31 to 54 days.     

Use of stomatal index as a marker to screen backcross populations of two wild potato species segregating for freezing tolerance

The purpose of this study was to investigate differences in stomatal index among backcross progeny ofSolanum commersonii (freezing tolerant) andSolanum cardiophyllum (freezing sensitive) to assess the feasibility of using this trait as a marker for screeningSolanum populations for freezing tolerance. Measurements were taken on three terminal fully-expanded leaflets per genotype by completing microscopic examination of epidermal impressions made in partially dissolved cellophane tape. Freezing tolerance was estimated in parallel studies on the same plant material. Values of SI were significantly greater (Fisher T-test, 0.05) for theS. cmm. group (parent + backcross progeny) compared with theS. cph. group. Stomatal index of the F₁ was significantly greater than SI ofS. cph. parents and similar toS. cmm. parents. Values of SI for both backcross progenies were greater than parental values. Non-acclimated relative freezing tolerance values were in the following order:S. cmm. parents >S. cmm. backcrosses > F₁ >S. cph. back-crosses >S. cph. parents. Stomatal index values followed a similar pattern with the exceptionS. cmm. backcross >S. cmm. parents. These data suggest: a) increased SI is inherited as a dominant trait, b) SI may be a useful screening marker in breeding programs interested in improving freezing tolerance.