QTL Mapping for Gummy Stem Blight Resistance in Watermelon (Citrullus spp.)

Abstract

Watermelon (Citrulluslanatus) is an economically important fruit crop worldwide. Gummy stem blight (GSB) is one of the most damaging diseases encountered during watermelon cultivation. In the present study, we identified quantitative trait loci (QTLs) associated with GSB resistance in an F2 population derived from a cross between maternal-susceptible line ‘920533’ (C. lanatus) and the paternal-resistant line ‘PI 189225’ (C. amarus). The resistance of 178 F2 plants was assessed by two different evaluation methods, including leaf lesion (LL) and stem blight (SB). To analyze the QTLs associated with GSB resistance, a linkage map was constructed covering a total genetic distance of 1070.2 cM. QTL analysis detected three QTLs associated with GSB resistance on chromosome 8 and 6. Among them, two QTLs, qLL8.1 and qSB8.1 on chromosome 8 identified as major QTLs, explaining 10.5 and 10.0% of the phenotypic variations localizing at same area and sharing the same top markers for both LL and SB traits, respectively. A minor QTL, qSB6.1, explains 9.7% of phenotypic variations detected on chromosome 6 only for the SB trait. High-throughput markers were developed and validated for the selection of resistant QTLs using watermelon accessions, and commercial cultivars. Four potential candidate genes were predicted associated with GSB resistance based on the physical location of flanking markers on chromosome 8. These findings will be helpful for the development of watermelon cultivars resistant to GSB.

QTL associated with Gummy Stem Blight (GSB) resistance in watermelon

“…have been reported to carry sources of GSB resistance. Resistance to GSB in cucurbits has been described to be monogenic dominant, monogenic recessive and polygenic [14,15]. For example, GSB resistance in 'PI 189225' was regulated by a single gene, db [11], however, new study revealed the involvement of numerous genes with environmental variables for GSB resistance [4].…”

“…Genetic studies of these resistant genotypes indicated various genetical control of resistance to GSB including monogenic control in PI 189225 in previous study [11] and polygenic control with minor effects from individual genes in PI 189225, PI 482283, and PI 526233 [4,12,13]. Several studies have mapped the QTLs underlying GSB resistance in watermelon, including one QTL on chromosome 8 of PI 189225 explaining 32% of the phenotypic variations [13]; three QTLs on chromosomes 3, 5 and 7, explaining between 6.4 and 21.1% of the phenotypic variation [14] and another three QTLs on chromosomes 8 and 6 [15]. Besides, QTLs for GSB resistance have also been identi ed in other cucurbits such in Cucumber [16,17] and melon [12,18].…”

“…GBS and ddRAD-seq techniques have been used for mapping genes and development of markers in several plant species such as rapeseed, soybean, maize, strawberry and melon [22][23][24][25]. High throughput molecular markers for GSB resistance have been reported in watermelon [14,15]. However, these markers were based on C. amarus and hence, are often not effective on C. lanatus.…”

Qtl Associated With Resistance to Stagonosporopsis Citrulli in Citrillus Amarus

“…The QTL mapped by the two studies on chromosome 8 are distinct from one another. The species of Stagonosporopsis used by Lee et al (2021) is unknown. Gimode et al (2021) used a population derived from Crimson Sweet (C. lanatus) × PI 482276 (C. amarus) and S. citrulli isolate 12178A to map GSB resistance QTL on chromosomes 5 and 7 17 .…”

“…Ren et al (2019) used a population derived from K3 (C. lanatus) × PI 189225 and an isolate of S. cucurbitacearum to map a GSB resistance QTL on chromosome 8 15 . Lee et al (2021) used a population derived from 920533 (C. lanatus) × PI 189225 and "D. bryoniae 'KACC 40937 isolate'" to map GSB resistance QTL, two on chromosome 8 and one on chromosome 6 16 . The QTL mapped by the two studies on chromosome 8 are distinct from one another.…”