Early Vigor Comparison Among Wheat Cultivars And Recurrent Selection Populations

Improving early vigor is very important for wheat grown under dry climates. The wheat breeding of for stronger early vigour is helpful to increase water-and nutrient-use efficiency, and weed competitiveness to profitably raise crop yields. Scientists in CSIRO (Commonwealth Scientific and Industrial Research Organisation) Agriculture Flagship have developed recurrent selection populations by randomly intercrossing a genetically diverse set of 28 vigorous wheat lines identified globally. The plants of S1:2 progenies with the widest 1 and 2 leaves were further intermated to develop new populations for assessment of early growth. This procedure was repeated for up to 60 segregating families per cycle across six cycles over 15 years. These recurrent selection populations and their parents as well as some Australian commercial cultivar were used in this study to analyze the factors affecting on wheat early vigor, to compare the traits of seedling and root morphology among individual cycles of recurrent selection, and to investigate early vigor of recurrent populations at different generations. The main research results are as follows: Early vigor within a genotype is affected by seed morphological traits. The comparison of early vigor within a genotype showed that embryo area, total and single leaf area, and seedling dry weight showed a linear positive correlation with seed weight. Among the analyzed nine wheat cultivars or lines, CV46 showed the highest regression co-efficiences of 0.09 and 3.55 between seed weight and embryo area and between seed weight and seedling dry weight, respectively. Cultivar Sunstate had a highest co-efficienceof 0.06 between seed weight and average leaf width. As the seed weight of increased, however, specific leaf area (SLA) didn’t accordingly increase within a genotype although there were differences between cultivars or lines, with a highest SLA of 0.28cm2/g for the wheat line VMeS2-The integrity of endosperm is another factor affecting early vigor. The influence of endosperm integrity on seedling’s early phenotypes was shown by that the remove of endosperm ratio from 0% to 40% was negatively correlated with early vigor. As endosperm reduced by 10%, first leaf area, seedling dry weight, leaves number, and dry weight of roots decreased 0.16 mm2,19.30 mg,0.04, and 18.83 mg, respectively. It was therefore assumed that wheat’s early vigor was affected by multiple factors besides embryo area.During recurrent selection processes, the factors of early vigor such as embryo area, mean leaf width, and overall dry weight showed a linear positive relationship with the cycle number. The differences between cycle number and some root morphological traits were not significant among the 6 populations, but these traits were better than commercial cultivars. The most vigorous wheat seedlings were identified in later cycles, with some lines producing more than double the leaf area and biomass of elite commercial wheat varieties. Phenotypic selection for greater leaf width was associated with a realized significant (P<0.01) linear increase per seedling of 0.57 mm per cycle (+9.8%) for mean leaf width, and correlated linear increases in total leaf area and biomass of 4.48 cm2 per cycle (+10.3%) and 10.8 mg per cycle (+5.3%), respectively. Genetic gains in widths of leaves 2 (+8.4%) and 3 (+11.5%) were significantly (P<0.01) greater than for leaf 1 (+5.3%). Selection for greater leaf width was associated with linear increases in coleoptile tiller leaf area, small curvilinear increases in leaf 1 length, and reductions in numbers of leaves and main stem tillers. By analyzing the traits of adult-plant stage, the result showed that correlated linear increases in main stem height and thousand seeds weight were 3.51cm (5.5%) and 2.17 (6.2%) per cycle, respectively and relative anthesis date reduced 1.08d per cycle.Development status of root reflects the strength of wheat’s growth vigor during its seedling stage to some extents. Strong roots provide sufficient nutrition and water during wheat’s seedling stage in a rainfed cultivation environment. With the increase of the recurrent times, the total dry weight of roots increased. However, the comparison of root’s phenotypes indicated that the proportion of dry weight of roots to that of whole seedling was negatively linearly correlated with numbers of generations among recurrent selection populations, while the proportion of dry weight of leaves to that of total seedling was positively correlated. A reduced ratio of 0.52% per cycle for root biomass of whole seedling was contrast with the increased leaf ratio of 0.44%. Moreover, root length and root hair’s density among recurrent populations were evidently higher than those of commercial cultivars.In recurrent selection processing the changes of early vigor were significant from the first to the sixth generation (Cycle 6) and the early vigor of Cycle 6 exhibited an extremely advantage on the traits of early vigor. We analyzed a reconstructed population (RSB, Recurrent selection B) using lines with early growth vigor and found that early vigor has a high inherited ability that can be used for future breeding. Recurrent selection, a simple, inexpensive, and repeatable selection process, provides a value method for developing vigorous wheat germplasm that can be used as parents in commercial breeding.