Pod Shattering Resistance Research Articles

Aligning a New Reference Genetic Map of Lupinus angustifolius with the Genome Sequence of the Model Legume, Lotus japonicus

We have developed a dense reference genetic map of Lupinus angustifolius (2n = 40) based on a set of 106 publicly available recombinant inbred lines derived from a cross between domesticated and wild parental lines. The map comprised 1090 loci in 20 linkage groups and three small clusters, drawing together data from several previous mapping publications plus almost 200 new markers, of which 63 were gene-based markers. A total of 171 mainly gene-based, sequence-tagged site loci served as bridging points for comparing the Lu. angustifolius genome with the genome sequence of the model legume, Lotus japonicus via BLASTn homology searching. Comparative analysis indicated that the genomes of Lu. angustifolius and Lo. japonicus are highly diverged structurally but with significant regions of conserved synteny including the region of the Lu. angustifolius genome containing the pod-shatter resistance gene, lentus. We discuss the potential of synteny analysis for identifying candidate genes for domestication traits in Lu. angustifolius and in improving our understanding of Fabaceae genome evolution.

Identification of variability in phenological responses in canola-quality Brassica juncea for utilisation in Australian breeding programs

Canola-quality Brassica juncea is a potential alternative crop species in lower rainfall Australian environments due to its superior heat and drought tolerance, disease resistance, and pod-shatter resistance compared with the currently grown B. napus species. Canola-quality types of B. juncea that are adapted to flower and mature before water deficits and high temperatures significantly limit yield potential are currently being developed. In this study, the variability in phenological characteristics in canola-quality B. juncea is assessed, with a view to identifying the potential for including a range of genetic phenological controls on the development of the crop to assist with adaptation. Vernalisation response was compared among 17 lines of B. juncea and 3 of B. napus, using a cold treatment of 2.6°C for 25 days. Leaf number, and duration to first flower and maturity were compared in response to the vernalisation treatments. To assess day length response, the same 20 genotypes were sown at five locations with a range of sowing times, and one controlled environment, where day length was artificially extended. Development stages were assessed and the duration of particular phenological phases determined in relation to time, thermal time, and photoperiod. The major factor controlling flowering in canola-quality B. juncea genotypes was day length, with only small responses to vernalisation detected. There was sufficient variability in these traits and in thermal time to flowering under long days (intrinsic earliness) within the current canola-quality germplasm in Australia to select early flowering genotypes with potential adaptation to low-rainfall environments.

Pod shatter resistance evaluation in cultivars and breeding lines of Brassica napus, B. juncea and Sinapis alba

AbstractPod shatter susceptibility was investigated in Brassica napus germplasm and shatter resistant species of B. juncea and Sinapis alba. The comparisons were made by measuring seed yield in field plots, detached pod rupture energy (RE) and the half‐life of pod‐opening. Pod shatter resistance was significantly greater in B. napus lines derived from interspecific hybridizations of B. napus with B. rapa, B. carinata and B. juncea, than common B. napus cultivars. While these lines exhibited no significant difference in resistance to pod shatter than B. juncea, an entry of S. alba had no yield loss caused by pod shatter. Resistance to pod shatter was characterized in the field as little or no yield loss after full maturity, delayed shattering in time, and stable yield performance under variable climatic conditions during pod maturity. Yield loss caused by pod shatter ranged from a low of 4% for the B. juncea cv. ‘AC Vulcan’ to a high of 61% for the black seeded B. napus line DH12075 in 2‐year field trials after 1 month maturity. Pod shatter resistance was not significantly associated with specific plant and pod morphological traits, except pod length (P = 0.005) in tested materials. Field visual scores of pod shatter through inspections of average pod shatter per plant within plots were highly correlated with plot yield loss. Indoor quantitative evaluations of pod strength using a pendulum machine to measure pod RE and random impact test to measure half‐life of pod‐opening resistance were highly correlated with field yield loss. Multiple evaluations of pod shatter in method and in time after pod maturity are recommended for reliable evaluation of pod shatter resistance.

Using novel variation in Brassica species to reduce agricultural inputs and improve agronomy of oilseed rape—a case study in pod shatter resistance

AbstractOilseed rape is a very undeveloped crop with regard to efficiency of production and the agronomic practice used to maximize its potential. The genetic potential to modify oilseed rape is limited by the narrow genetic base found within the breeding gene pool, resulting in limited novel variation available for exploitation. Novel variation is, however, present in wild diploid ancestors of oilseed rape and has been made available by developing synthetic Brassica napus. This is illustrated through the use of this material to develop an understanding of pod shattering which is one of the most agronomically important characteristics of the crop. Through a variety of approaches it is shown how progress has been made to understand this trait and how this understanding is being used to improve the crop such that efficiency of production will be enhanced.

Pod shatter resistance in the resynthesized Brassica napus line DK142

Resistance to pod shatter was studied within and between populations of the resynthesized Brassica napus line DK142, grown under glass or in the field, at sites in the UK and Belgium. All populations showed similar ranges of resistance that were greater than that of a commercial cultivar (Apex). The increase in range was at least three-fold greater than the range found in Apex. Only sowing time affected the descriptive statistics of shatter resistance of each line, with spring-sown populations more shatter susceptible than winter-sown populations. The partitioning of dry matter to individual tissues of the pod was different for the two lines, with dry matter biased to the seed in Apex and to the receptacle in the more resistant DK142. In DK142 and Apex, as well as F1 and F2 populations derived from crosses between DK142×Apex, correlations for pod shatter resistance and mature pod characters were high, particularly the weight and length of the valves and septum. Shatter resistance increased in plants when pod numbers were reduced by the removal of whole racemes.

Breeding oilseed rape for pod shattering resistance

The genetic control of pod dehiscence was studied through the production, field trial and subsequent analysis of a full diallel involving seven parents selected for high and low resistance to pod shattering. Additive gene effects were most significant among the measures of pod shattering resistance with only minor contributions from non-additive gene effects. Genetic variation in measures of the stiffness of the pod wall were, however, determined by dominant gene effects. Genes for increased pod shattering resistance acted recessively. All characters showed high levels of heritability. Correlations among pod shatter resistance characters and other pod, raceme and plant characters were low suggesting that resistance is likely to be independent of other important agronomic traits.

Genetic variation for pod shatter resistance among lines of oilseed rape developed from synthetic B. napus

Variation for a wide range of plant characters, more extensive than that normally found in oilseed rape, has been characterised within a Brassica napus genetic background developed from three synthetic lines of B. napus which had been produced previously from crosses between wild diploid B. oleracea and wild diploid B. rapa species. These synthetic lines were crossed with three oilseed rape cultivars from which were produced three doubled haploid populations of B. napus. These populations were grown as spaced plants in the field and measurements made on plant, raceme and pod architecture so that any new variation could be assessed. Laboratory procedures have been developed to measure the level of resistance to pod shattering among these populations and to determine the mechanical properties of these pods. Resistance to pod shattering determined in the laboratory was broadly linked to field assessment scores. Genetic variation in pod shattering resistance which exceeded that found among a selection of modern cultivars has been found among lines of these populations. This variation is associated with the particular diploid Brassica parents used to make the synthetic oilseed rape. There are no significant associations among the measured plant characters except for that between beak length and the force needed to shatter the pods as determined in laboratory tests. This suggests that it should be possible to select for resistance to shattering independently of other agronomic characters. Resistance to shattering appears to be linked to a failure of the dehiscence zone's cells to degrade and to the presence of extra vascular tissue within this zone.

Application of the ideotype concept in breeding for higher yield in the oilseed brassicas

Approaches to yield-improvement breeding methodology which utilize information from biometrical genetic studies and from plant physiological studies aimed at developing ideotype models are reviewed here, with special emphasis on yield improvement in the oilseed brassicas. Major difficulties involved in yield-improvement programmes are the accurate selection of parents from which to generate superior breeding populations, and the selection of high-yielding genotypes from early-segregating generations. In both cases, the complex polygenic inheritance of yield and the magnitude of genotype × environment interactions affecting yield greatly reduce the chances of isolating superior genotypes. A wide array of biometrical procedures have been proposed in developing yield-improvement programmes. Some have been utilized successfully. However, their use in analyzing a character such as yield has been generally limited because of the need to conduct analyses with populations sown at much lower densities than commercial crops. Development of the ideotype concept has focussed the attention of plant physiologists on identification of simple morphological characters which have some influence on physiological processes determining the yield of the economic organs. Characters such as leaf inclination and leaf shape, for example, are often simply inherited and can greatly influence crop canopy structure and radiation interception. Such characters could be rapidly modified by selection to increase crop photosynthesis and yield. Ideotype definitions integrate information on these relationships and provide plant breeders with a clear blueprint of the characteristics of a high-yielding cultivar in a specified environment. Research with oilseed Brassica species in Western Australia and Tasmania has identified a number of highly heritable characters which provide a basic framework for the definition of a yield ideotype for spring rape ( B. napus). These include an optimal time of flowering, apetalous flowers and long upright pods to improve light penetration of the dense pod canopy, and pod shattering resistance to allow for direct harvesting of the crop. A major advantage in breeding for this ideotype is that genes for certain characters can be easily introgressed from the related species B. campestris and B. juncea. It is also possible, using microspore cultures, to generate large numbers of B. napus pure lines directly from plants selected in F2 populations on the basis of ideotype characteristics. This would allow for large-scale yield testing of selections within two to three years of making the original crosses.