Physiological and Pathological Basis of Disease Resistance for the Wheat Stay-Green Mutant Tasg1 to Infection by Fusarium graminearum

A wheat stay-green mutant, tasg1, was previously generated via mutation breeding of HS2, a common wheat cultivar (Triticum aestivum L.). Compared with wild-type (WT) plants, tasg1 plants showed slower degradation of chlorophyll. To study the disease resistance of tasg1, tasg1 and its WT Hesheng 2 were used as materials in the experiment. Disease stress was induced by Fusarium graminearum. Disease stress inhibited the growth of both tasg1 and WT wheat seedlings, but the inhibition was milder in tasg1 than in WT plants. The results indicated that tasg1 plants have higher chlorophyll content, actual efficiency (ФPSII), maximal photochemical efficiency of PSII (Fv/Fm), and net photosynthetic rate than WT plants under disease stress. Disease stress resulted in significant decreases in water potential (Ψw), osmotic potential (Ψs), and relative water content (RWC) in both wheat varieties, but the decreases were greater in WT than in tasg1 plants. Furthermore, the osmolyte content (soluble protein content, soluble sugar content and free proline) in tasg1 was greater than that in the WT under disease stress. Tasg1 plants had less oxidative damage, as indicated by MDA content, relative electrical conductivity, O₂^• - production rate and hydrogen peroxide. This improved performance of tasg1 plants was accompanied by greater increases in superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX). Our results suggested that the stay-green wheat mutant tasg1 has higher disease tolerance than WT plants. The higher antioxidant competence of tasg1 plants may play an important role in their enhanced disease tolerance.