Bipolaris sorokiniana causes spot blotch on leaves, root and crown rots, node cankers and seedling blight on wheat (21 ). Early symptoms on leaves are characterized by small dark brown lesions 1 to 2 mm long without chlorotic margin. In susceptible genotypes, these lesions extend very fast into oval to elongated blotches, light brown to dark brown in colour, reaching several cm long before coalescing and inducing the dead of the leaf. However, disease expression has been reported to be modulated by abiotic factors such as soil fertility and moisture stresses (15, 16), high temperature(7), as well as by biotic factors such as pathogen virulence (9, 11, 13), leaf age (11, 18) and plant growth stage (4, 5).Progressive breakdown of resistance between GS 69 (anthesis completed) and GS 77 (late milk grain) leads to the increased production of conidia on the increasing amount of senescing tissues of wheat plants and thus of the conidial population of B. sorokiniana under field conditions (4). Nevertheless, no evidence has been published regarding the modulation of resistance to one or more of the B. sorokiniana phytotoxins during plant developmental stages. In culture media B. sorokiniana is producing several sesquiterpenoids toxins, the most important being helminthosporol (HL). It has been shown that this metabolite, together with its dialdehyde analogue, helminthosporal were the substances responsible for inducing the plant disease symptoms (6). More recently, it has been suggested that the precursor prehelminthosporol (PHL) is the main substance responsible for the biological phytotoxicity (3), affecting the activity of enzymes located on the plasma membrane and disrupting cell membranes (1,2). Similarly, HL is supposed to play an important role in pathogenesis by killing or weakening plant cells in advance of the growing hyphae (2). Evidence of strong effects in decreasing cell permeability of 1-mM HL toxin solution were reported by different authors (2, 19). HL has a non-specific membrane disrupting effect (2), but the correlation between HL sensitivity and known B. sorokiniana resistance levels in wheat cultivars has not yet been studied (12). This study was undertaken to test the hypothesis that the plant developmental stages influence the disease expression of wheat genotypes differing in their genetic background regarding maturity and spot blotch resistance when inoculated at similar growth stages with B. sorokiniana, and to evaluate, under controlled environmental conditions the correlation between the disease reaction and the HL sensitivity at various developmental stages.

Research and Partnership Program

English

0407|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

INT1237

CIMMYT Staff Publications Collection