ANNOUNCEMENTS
Spot blotch (causative pathogen Bipolaris sorokiniana) is a highly destructive foliar disease of wheat (Triticum aestivum L.), which is important mainly in warm, humid growing conditions. Two spot blotch resistant QTLs located on Chromosome 2BS and 5BL were dissected in to single Mendelian gene using 341 single seed descent (SSD) derived F3 and F4 lines of “YS102 × Sonalika” and 335 F3, F4 and F5 lines of “YS116 × Sonalika” cross respectably. Both the SSD derived populations were tested for spot blotch resistance under artificial epiphytotic conditions in the field BISA, Pusa Bihar; a hot spot for spot blotch. Disease severity (%) and AUDPC values were calculated for each line. Lines tested from F3 to F5 were inoculated in the field with B. sorokiniana over three consecutive seasons. Measurements of both disease severity and the area under the disease progress curve were used to assess each line's disease response. These lines were developed by using a RIL, YS102 and YS116 (F12) of the ‘’Yangmai 6 × Sonalika’’ cross as resistant parent and ‘Sonalika’ as the susceptible parent. The resistant parent ‘YS102’ and ‘YS116’ were selected on the basis of phenotypic data and presence & absence of the alleles linked to spot blotch resistance. The parent YS116 was known to possess a single major QTL on chromosome 5BL while YS102 possess QTL on chromosome 2BS. The test for goodness of fit (1:2:1 in F3, 3:2:3 in F4 and 7:2:7 in F5 generation) confirms the segregation at one locus for both the crosses. These SSD derived lines from both the crosses may further use for Fine mapping and Map based cloning for spot blotch resistant QTLs.
Quantitative trait locus (QTL) QSb.bhu-5B, which determines resistance to spot blotch, was mapped to an interval of 0.62 cM on chromosome arm 5BL via the analysis of a recombinant inbred line population bred from a cross between ‘YS116’ and ‘Sonalika’. In the present population, QSb.bhu-5B, which is flanked by the SSR loci Xgwm639 (0.28 cM) and Xgwm1043, behaved as a single Mendelian gene, and was given the gene symbol Sb2. The physical location of Sb2 is within the 5BL1-0.55-0.75 deletion bin. Both Xgwm1043 and Xgwm639 were effective as indirect selection tools in various genetic backgrounds.
Not only the aims set out for this study were achieved by dissecting and enriching the QSb.bhu-5B QTL with new markers but a close association of spot blotch disease resistant QTL on chromosome 7D was found with the markers linked to Lr34 (ABC transporter) gene and Pm34/Yr18/LTN gene complex. A total of 94 near isogenic lines (NILs) including parents derived from the cross of two 'Jupateco' sister lines (Lr34+ and Lr34-) were evaluated for the Spot blotch, leaf rust and stripe rust. Leaf tip necrosis (LTN) was recorded for the presence and absence. A high correlation between the spot blotch, leaf rust and strip rust resistance was found. SWM10 was found to be linked to spot blotch disease resistant QTL on chromosome 7D which was in a close association with cslv34, a diagnostic marker for Pm34/Yr18/LTN gene complex.
Evaluation of wheat for spot blotch disease resistance relies on various visual observation methods. The person who evaluate lines need to be experienced to score disease severity. To facilitate high-throughput phenotyping, hand-held green seeker NDVI sensor was used to map spot blotch disease resistance QTL. A total of 108 germplasm lines along with 335 SSD derived lines (F4 and F5 generations) originating from the cross ‘YS116 × Sonalika’ were used. The population was evaluated at BISA, Pusa Bihar; a hot spot for spot blotch, for two consecutive years. Data was recorded using NDVI as well as by visual observation as % disease severity. Correlation coefficient was calculated between two scoring methods (NDVI and % DS) recorded at different growth stages. High negative correlation was observed between NDVI and % DS at GS69 and GS77 on Zadoks scale. With both methods, the QTL was mapped in the same chromosomal region on 5BL. Using NDVI value, the detected QTL explained up to 54.9% of phenotypic variation while up to 56.1% using % DS
Shodhganga Link
