Screening sorghum genotypes for salinity tolerant biomass production

Genetic improvement of salt tolerance is of high importance due to the extent and the constant increase in salt affected areas. Sorghum [Sorghum bicolor (L.) Moench] has been considered relatively more salt tolerant than maize and has the potential as a grain and fodder crop for salt affected areas. One hundred sorghum genotypes were screened for salinity tolerance in pots containing Alfisol and initially irrigated with a 250-mM NaCl solution in a randomized block design with three replications. Subsequently 46 selected genotypes were assessed in a second trial to confirm their responses to salinity. Substantial variation in shoot biomass ratio was identified among the genotypes. The performance of genotypes was consistent across experiments. Seven salinity tolerant and ten salinity sensitive genotypes are reported. Relative shoot lengths of seedlings were genetically correlated to the shoot biomass ratios at all stages of sampling though the relationships were not close enough to use the trait as a selection criterion. In general, the whole-plant tolerance to salinity resulted in reduced shoot Na⁺ concentration. The K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were also positively related to tolerance but with a lesser r ². Therefore, it is concluded that genotypic diversity exists for salt tolerance biomass production and that Na⁺ exclusion from the shoot may be a major mechanism involved in that tolerance.     

Integrated breeding approaches for improving drought and heat adaptation in chickpea (Cicer arietinum L.)

Chickpea (Cicer arietinum L.) is a dry season food legume largely grown on residual soil moisture after the rainy season. The crop often experiences moisture stress towards end of the crop season (terminal drought). The crop may also face heat stress at the reproductive stage if sowing is delayed. The breeding approaches for improving adaptation to these stresses include the development of varieties with early maturity and enhanced abiotic stress tolerance. Several varieties with improved drought tolerance have been developed by selecting for grain yield under moisture stress conditions. Similarly, selection for pod set in the crop subjected to heat stress during reproductive stage has helped in the development of heat‐tolerant varieties. A genomic region, called QTL‐hotspot, controlling several drought tolerance‐related traits has been introgressed into several popular cultivars using marker‐assisted backcrossing (MABC), and introgression lines giving significantly higher yield than the popular cultivars have been identified. Multiparent advanced generation intercross (MAGIC) approach has been found promising in enhancing genetic recombination and developing lines with enhanced tolerance to terminal drought and heat stresses.     

Photosynthetic Apparatus Responses to Short‐term low‐temperature Flooding May Contribute to Freezing Tolerance Changes in Forage Grasses

Winter conditions are subjected to rapid climate changes. Increased precipitation and snow melting during warmer winters may result in low‐temperature flooding. These factors probably affect plant overwintering strategies. This study investigated the relationships between the photosynthetic adjustment and freezing tolerance following a short‐term low‐temperature flooding in two forage grasses (Lolium perenne and Festuca pratensis). The effect of flooding on the photosynthetic apparatus acclimation to cold was determined using chlorophyll a fluorescence measurements. Freezing tolerance was estimated using an electrolyte leakage test. It has been shown that genotypes activating non‐photochemical mechanisms of photosynthetic acclimation to cold during low‐temperature flooding may show increased freezing tolerance. Freezing tolerance reduction observed in Festuca pratensis was probably connected with decreased photochemical activity and photoinhibition of photosynthesis. It can be concluded that photosynthetic apparatus response to low‐temperature flooding may contribute to changes in the freezing tolerance. The direction of the changes is associated with different photosynthetic apparatus performance.     

Attempts to overcome partial incompatibility between Hordeum vulgare L. and H. bulbosum L.

Summary Partial incompatibility has already been reported between Hordeum vulgare and H. bulbosum during the course of doubled haploid production, and in this paper attempts to overcome the breeding barrier are described. The methods which seem to offer most success are those of environmental adjustments and the adoption of new genotypes of H. bulbosum. Further cultivars of H. vulgare exhibiting this phenomenon are also noted.     

Studies for assessing the influence of hardening on cold tolerance of barley genotypes

Summary Frost tolerance of 30 barley (Hordeum vulgare L.) cultivars have been field evaluated in North Italy during the 1990/1991 winter season that was characterized by exceptionally low temperatures without snow cover. The results showed a significant correlation between cold injury and grain yield loss (r=0.61^**). Five cultivars chosen for their varying degree of frost tolerance were further evaluated using laboratory tests. Measurements of survival rate and membrane damage were used to assess the influence of hardening on frost resistance. The reliability of the tests is shown by the high correlation to the field data. For both the laboratory temperature regimes and field conditions, the tested cultivars showed the same order of classification. The effect of a rise in temperature at the end of the hardening treatment on frost tolerance is also reported. The laboratory tests here proposed can be integrated in a breeding programme for improving frost tolerance in barley.     

水稻基部伸长节间性状与倒伏相关性分析及QTL定位

利用珍汕97B/密阳46 RILs群体及其构建的连锁图谱，对水稻株高和基部Ⅰ、Ⅱ伸长节间性状与稻株抗倒伏能力进行相关分析，并对基部Ⅰ、Ⅱ伸长节间性状进行QTL定位，共检测到加性效应QTLs 16个、加性´加性互作33对。估算了每个QTL的加性效应值和每对加加互作的上位性效应值，比较了QTLs的基因组分布。在第1染色体短臂和第     

Evaluation of a semi‐controlled test as a selection tool for frost tolerance in durum wheat (Triticum durum)

Most durum wheat (Triticum durum) varieties possess only low winter hardiness due to their frost susceptibility. In North America and Central Europe, durum wheat is therefore typically sown in spring to circumvent the local winter conditions. However, the yield potential of durum in these regions could be much better exploited if durum varieties with increased frost tolerance were available, which could be sown in autumn. A factor limiting breeding for increased frost tolerance is the variation in the occurrence of frost stress across years. The ‘Weihenstephaner Auswinterungsanlage’ is a semi‐controlled test that exposes the plants to all weather conditions. Snow coverage of the plants, serving as frost protection, is prevented by the movable glass lid of the semi‐controlled test. In this study, different scorings for frost tolerance based on this semi‐controlled test were evaluated and compared with frost tolerance data in the field. Our results illustrate the potential of the ‘Weihenstephaner Auswinterungsanlage’ as an indirect selection tool for frost tolerance in durum breeding programmes, especially when regular frost tolerance data from the field are not available.     

Evaluating different bahiagrass cytotypes for heat tolerance and leaf epicuticular wax content

Summary Bahiagrass (Paspalum notatum Flugge) is a polymorphic species indigenous to South America which has become naturalized in the southeastern U.S. The most common form in the United States is Pensacola bahiagrass,P. notatum var.saurae Parodi., which is a valuable forage. Pensacola is a sexual diploid, while most other bahiagrasses are apomictic tetraploids. Pensacola bahiagrass is considered to have greater heat tolerance (based on anin vitro heat tolerance test) than a number of otherPaspalum species, but has less leaf epicuticular wax (a drought avoidance mechanism) than other species. Both heat tolerance and leaf epicuticular wax are desirable characteristics for species grown where periodic drought occurs. We measured both characteristics over two years in a collection of 23 bahiagrass accessions, many of which had been collected in South America near the center of origin of the species. The collection included various ploidy levels. For both years, no accessions ranked statistically lower in damage in the heat tolerance test than Pensacola, although eight had significantly higher damage. Two entries in addition to Pensacola had very low damage in the heat tolerance test. Pensacola was high in leaf wax, with 16 accessions rated significantly lower in wax. The accession having the lowest wax content was a triploid, which also exhibited considerable leaf death in the field in response to drought and heat. The diploid entries tended to be higher in leaf wax than the other ploidy levels. This study has identified additional bahiagrass germplasm which may be of use in a breeding program.     

Identification of quantitative trait loci for agronomic and physiological traits in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under high-nitrogen and low-nitrogen conditions

Low-nitrogen (LN) tolerance is a compound character with a complex genetic basis. Many agronomic traits have been shown to be closely related to LN tolerance in maize. In this study, 150 F₇ recombinant inbred lines derived from a cross between inbreds 178 and K12 were evaluated for agronomical and physiological traits under high-nitrogen (HN) and LN conditions in 2 years. Inclusive composite interval mapping (ICIM) was used to identify the quantitative trait loci (QTLs) for traits recorded under different treatments (LN and HN) in 2 years. In total, 86 QTLs were detected: 38 for HN and 35 for LN, while 13 QTLs were detected under both nitrogen levels, suggesting that LN-specific QTLs may play a role in improving LN tolerance in maize. Overlapping QTLs for different traits were located on all chromosomes except chromosome 4 and chromosome 9. Many of these regions overlapped with previously reported QTLs. Several consensus major QTLs and LN-specific major QTLs found in the study can be used in marker-assisted selection breeding for genetic improvement and LN tolerance in maize in the future.     

Diversity and adaptation in rice varieties under static (ex situ) and dynamic (in situ) management

This study compares genebank-conserved and farmer managed populations of the same farmers' varieties of rice. Seven varieties that had been collected twice, in the early 1980s and in 1991, were recollected in 1997 after having been grown continuously in farmers' fields. Since the first genebank collection, rice cultivation in the Meking delta has been intensified with a rather abrupt switch from single to double cropping, more use of chemical fertilisers, improved water management, and more market oriented production. Many farmers' varieties have been maintained as a second crop but with a considerably delayed planting time compared to previous practice. In this experiment, the ex situ materials represent adaptation to pre-intensification conditions while the in situ populations have been exposed to the intensive production system for a number of years. The materials were tested in the wet season of 1997 under current farmers' management practices in an on-farm field experiment within the area where the varieties originated. Agronomic, stress resistance and morphological traits and variation at 7 isozyme loci were observed in the field or laboratory. Analysis of variance (ANOVA) and Principal Component Analyses (PCA) were used to study differences in agronomic and morphological traits between ex and in situ populations. Isozyme variation was analyzed by Nei's diversity indices and Wright's F-statistics. Farmer-managed populations showed a general trend of later flowering and maturity time, more uniformity of grain quality, lower frequency of undesired off-types, and reduced drought stress tolerance compared with corresponding ex situ populations. There were no significant differences in grain yield or tolerance to biotic stresses. Allelic frequencies of isozymes showed no consistent differences that could be related to changes of the farming system. These results are interpreted as an adaptation to the changed farming system and include natural and farmers' selection for maturity time (all varieties are photoperiodic)and market standards. The poorer drought tolerance may reflect the fact that such stress was common before intensification but is not normally a factor under the current water management regime. For in situconservation strategies this case sheds some light on the survival of allelic diversity vs. adaptedness. Isozyme data indicate maintenance of allelic diversity. Adaptedness, however, is at risk under on-farm conservation. Natural and intentional selection will normally not remain constant over time. Consequent genetic changes include loss of adaptation to past conditions and building up of adaptation to new. In this case such changes have happened surprisingly fast. However, changes are limited to adaptation to factors of the environment and to market-relevant quality traits. Yield seems to be unaffected. Considering needs for crop improvement this case has kept the materials `updated' with respect to adaptation and unchanged with respect to yield potential. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of new QTL for salt tolerance from rice variety Pokkali

Salt stress is an ever-present threat to rice production worldwide. Rice salinity tolerance is complex, both genetically and physiologically. The success and effectiveness in selecting salt-tolerant rice variety require the identification of QTL for the tolerance and closely linked molecular markers. In the present study, a RIL population consisting of 148 lines, derived from a cross between IR29 (salt-sensitive) and Pokkali (salt-tolerant), was used to identify new QTL for salt tolerance and investigate the relationships between salt stress caused injury and the changes in different physiological and morphological traits at the seedling stage. 14,470 high-quality SNP markers generated by the Rice 56K SNP array were converted to 1,467 bin markers for linkage mapping. A high-density genetic linkage map covering 1,680.9 cM was constructed, with the physical to genetic distance ratio being 222 Kb/cM. In total, 23 QTL for different salt tolerance indices were identified, including the previously reported Saltol which is currently used in breeding programmes. Three QTL for salt injury score (SIS) were located on chromosomes 1, 4 and 12, all being closely related to the long-distant Na⁺ transport from roots to shoots. These QTL showed additive effects, thus can be effectively used in breeding programme to pyramid various tolerance genes.     

Breeding for improved drought tolerance in Chickpea (Cicer arietinum L.)

Chickpea (Cicer arietinum L.) is an important legume crop as a protein source across the world. It is mostly grown on arid and marginal lands where it faces drought stress at different growth stages. Drought stress exerts drastic effects on nutrient uptake, hinders the nodule formation and adversely affects yield and yield components. Generally drought at any growth stage and organizational level is responsible for reduction in economic yield. Significant variability in chickpea germplasm is present on the basis of responses to drought stress in the form of drought escape, drought avoidance and drought tolerance; these mechanisms prevent chickpea crop from harmful effects of drought. Improvement in chickpea germplasm against drought stress could be made by using several breeding approaches, that is introduction, hybridization, mutation breeding, marker‐assisted breeding and omic techniques. These breeding approaches, especially marker‐assisted breeding and omics, are further strengthened with the availability of the chickpea genome sequence. This review highlighted the significance, status and advances in different breeding strategies for improvement of drought tolerance in chickpea.     

Apparent preference by bees for different flower colours in cowpeas (Vigna sinensis (L.) Savi ex Hassk.)

Summary A strong preference for different cowpea flowers apparently due to colour is reported for bumble bees (Bombus spp.) and honey bees (Apis mellifera). Bumble bees visited purple flowers much more often than they did white flowers in a ratio of 3:1. Honey bees, on the other hand, visited white flowers more than they did purple flowers in a ratio of 2:1.Judged from the positioning of their heads in the flowers, bumble bees are generally nectar collectors while honey bees collect both pollen and nectar but more of the former.This strong preference has implications in experiments designed to estimate out-crossing where different flower colours are used in the detection of hybrid plants. There will be more intra-colour than inter-colour pollen transfer.     

Genetic control of frost tolerance in wheat (Triticum aestivum L.)

Summary The frost tolerance of winter wheat is one component of winter hardiness. If seedlings are frost resistant, it means that they can survive the frost effect without any considerable damage. To study the genetic control of frost tolerance, an artificial freezing test was used. Frost tolerance is controlled by an additive-dominance system. The results of diallel analyses indicate the importance of both additive and non-additive gene action in the inheritance of this character. The dominant genes act in the direction of lower frost tolerance and the recessive genes in the direction of a higher level of frost tolerance. The results of monosomic and substitution analyses show that at least 10 of the 21 pairs of chromosomes are involved in the control of frost tolerance and winter hardiness. Chromosomes 5A and 5D have been implicated most frequently. The geneFr1 (Frost 1) was located on the long arm of chromosome 5A. Crosses between cultivars, chromosome manipulation and the induction of somaclonal variation may be suitable methods for broadening the gene pool for frost tolerance.     

Alien species as sources of physiological traits for wheat improvement

Summary Enhanced levels of drought, cold and salinity tolerance plus leaf photosynthesis and high protein content have been identified in species of Agropyron (Elytrigia) and Triticum (Aegilops). Because these characters, is most cases, are products of numerous metabolic pathways, they likely will have complex inheritance patterns and therefore may be difficult to transfer to bread wheat. However, all of the alien species in question are crossable with wheat. Most of the hybrids have been made and in many cases the material has been advanced to the state of addition lines which are available for screening. Where adequate screening tests are available, breeding techniques such as recurrent selection should be effective in transferring the traits.Contribution No. 781 Ottawa Research Station.     

Location of genes controlling resistance to greenbug (Schizaphis graminum Rond.) in Hordeum chilense

Wheat/Hordeum chilense disomic addition lines have been used to locate genes influencing resistance against greenbug (Schizaphis graminum Rond.) in specific chromosomes of H. chilense. H. chilense is a source of antixenosis, antibiosis and host tolerance to the greenbug, being resistant also to the Russian wheat aphid, the two key pests in wheat. For measuring antixenosis, the numbers of aphids per plant were recorded in a host free choice test; antibiotic resistance was determined by measuring the developmental time, the fecundity and the intrinsic rate of population increase of aphids reared on the different hosts, and host tolerance to aphids was evaluated by the leaf damage and the number of expanded leaves on the hosts after 3 weeks of infestation. The greenbugs belonged to a clone of biotype C. Plant genes with positive effects for antixenosis were located on chromosome 1H^ch. Genes with positive effects for antibiosis were located on three different chromosomes and those that prolonged aphid developmental time were located on chromosomes 5H^ch and 7H^ch while those that reduced the total fecundity were on 4Hch. Chromosome 7H^ch accounted for host tolerance to greenbug.     

In vitro screening and field evaluation of tissue-culture-regenerated sorghum (Sorghum bicolor (L.) Moench) for soil stress tolerance

Summary Sorghum bicolor (L.) Moench is generally quite sensitive to salt and acid (high aluminium) soil stresses, but quite tolerant of drought stress. As with any stress phenomenon, intra-specific variability exists within the genus. In vitro cell selection and somaclonal variation offer an alternative to traditional breeding methodology for generating improved breeding lines for hybrid development. A field selection protocol was developed for the three soil stresses and inter-stress evaluations were conducted in an effort to find multiple, stress-tolerant genotypes. The acid soil-drought stress, super-tolerant selections were located by the R₇ generation when exposed to a combined aluminium-drought stress field environment and when the regeneration population (number of regenerated lines from one callus source) was maintained at 15,000 plants or higher. A variant frequency of 0.1 to 0.2% for stress tolerance and acceptable agronomic traits among the surviving somaclones, provided an adequate number of phenotypes with desirable agronomic characteristics and a high level of soil stress tolerance. Subsequent research verified that the stress-tolerant regenerants had superior acid soil and drought stress tolerance to that of the donor parents, that their yield capabilities under stress were superior to their parents, and that their stress tolerance attributes were transferred in hybrid combinations. In vitro selection was not effective in increasing the number of field stress survivors. In fact, superior germplasms were developed from non-stressed callus or salt-stressed callus. In vitro selection reduced regeneration frequency and subsequent survival of plants under field stress. In vitro-stressed regenerants should be subjected only to non-stressed environments to maintain population numbers for field selection and thereafter should be subjected to stress environments during later (R₅₊) generations. The optimal strategy for the exploitation of somaclonal variation may be through short-term cell culture (< 12 months) with no attempt at in vitro selection.     

Fluorimetric Determination of the Genetic Variability Existing for Chilling Tolerance in Sweet Sorghum and Sudan Grass

Chilling temperatures drastically inhibited the photochemical quenching of chlorophyll fluorescence (q_Q) measured in intact leaves photosynthesizing under steady-state conditions. This effect appeared, however, to be characteristic of chilling-susceptible plant species and was not observed in plants which are known to be chilling-tolerant, indicating that the measurement of q_Q can serve in practice to estimate rapidly the relative chilling tolerance of crop plants. A large number (28) of sweet sorghum (Sorghum bicolor) and Sudan grass (Sorghum sudanense) genotypes were screened for chilling tolerance using this rapid q_Q method. Although sweet sorghum and sudan grass obviously behaved as chilling-sensitive plants, a considerable variation for chilling susceptibility was observed among the different genotypes tested. Some sweet sorghum varieties, such as ‘Dale’ and ‘Keller’, and most of the sudan grass varieties appeared to possess a certain degree of resistance towards low temperature stress, indicating the existence of useful germplasms in Sorghum for improving stress tolerance.