Diaporthe sclerotioides exhibits no host specificity among cucurbit species

Abstract

Plant-fungal specificity between cucurbitaceous crops and Diaporthe sclerotioides, the causal agent of black root rot, was studied using cucumbers (Cucumis sativa), melons (Cucumis melo), pumpkins (Cucurbita maxima), watermelons (Citrullus lanatus) and bottlegourd (Lagenaria siceraria var. gourda). Twelve D. sclerotioides isolates from these cucurbit species were cross-inoculated. The virulence of the isolates was evaluated as the area under the disease progress curve (AUDPC). All cucurbit species were susceptible to each isolate, but AUDPCs were significantly different among the hosts, with the order of greatest to least being melon, cucumber, watermelon, bottlegourd and finally, pumpkin. The infectiveness of isolates was assessed as the quantity of D. sclerotioides DNA detected in the hypocotyls of seedlings 2 weeks after inoculation using a real-time PCR protocol. The fungal DNA quantities varied among the species in the same order as the AUDPCs. Whilst there were statistically significant correlations between the virulence and infectiveness of D. sclerotioides isolates in cucumbers, melons and bottlegourds, their coefficients of determination were not high (r 2 < 0Á6). Orthogonal contrasts indicated no specificity in either the fungal virulence or infectiveness between D. sclerotioides isolates and the cucurbit hosts from which these isolates originated. Thus, although the degree of host susceptibility to D. sclerotioides varies among cucurbit species, the absence of specificity to the host species in either virulence or infectiveness suggests the pathogen may spread via various cucurbit crops, irrespective of their original host species.

Root‐knot nematodes do not affect black root rot disease severity on watermelon and bottle gourd

“…As shown in this study, there are differences in susceptibility to black root rot among cucurbit species (Shishido et al ., ). Currently, all watermelon and bottle gourd cultivars are susceptible to black root rot.…”

“…Therefore, it seems likely that the results of this study are applicable to other cultivars of these cucurbit species. However, this investigation tested only one strain of D. sclerotioides , 59w, which is moderately virulent to watermelon and bottle gourd (Shishido et al ., ); thus, the disease‐promoting effects of M. incognita on black root rot by weakly virulent strains of D. sclerotioides remain to be investigated.…”

“…For inoculation, D. sclerotioides 59w was used, which had been isolated from a root of bottle gourd rootstock grafted onto a watermelon scion in Chiba, Japan. The isolate 59w exhibited moderate pathogenicity and virulence to both watermelon and bottle gourd (Shishido et al ., ). Meloidogyne incognita (race 2) was kept in successive cultures using live tobacco ( Nicotiana tabacum ‘NC 95’) at the Agriculture and Forestry Research Center of Chiba Prefecture.…”

“…Kachidoki‐2‐go) were germinated by incubating at 25 °C on moist filter paper for 3 days and then they were sown in a rhizobox filled with autoclaved vermiculite. A rhizobox is a thin container consisting of two glass plates (30 × 24 cm) separated by a gap of 8 and 12 mm for watermelon and bottle gourd, respectively (Shishido et al ., ).…”

“…Shishido et al . () reported that D. sclerotioides exhibits no host specificity in pathogenicity or virulence among bottle gourd ( Lagenaria siceraria var. gourda ), cucumber ( Cucumis sativus ), melon ( C. melo ), pumpkin ( Cucurbita maxima ) and watermelon ( C. lanatus ).…”