Natural and induced resistance of table grapes to bunch rots.
Sarig, P.; Zutkhi, Y.; Lisker, N.; Shkelerman, Y.; Ben-Arie, R.;
Acta Horticulturae Year: 1998 Issue: No. 464 Pages: 65-70 Ref: 10 ref.
1998
บทคัดย่อ
The effects of cultivar, berry growth, growth regulator application and tannin content on disease susceptibility of grapes was assessed. In cultivar Thompson Seedless, susceptibility to Rhizopus stolonifer and soluble solids content increased and skin thickness decreased (mainly due to changes in the thickness of the hypodermis) as berries developed. GA3 application (40 mg/litre at the 3-4 mm berry diameter stage) increased cell size in the epidermis (particularly in the hypodermis) and increased decay caused by R. stolonifer in several new seedless cultivars. CPPU [forchlorfenuron] application (5-10 mg/litre at the same stage) increased cell division, resulting in smaller cells, a higher cell density and a thicker skin, and reduced incidence of decay following inoculation with R. stolonifer. These results suggest that susceptibility to fungal invasion is related more to cell size or cell density in the skin layers than to absolute skin thickness; however, statistical analysis of all the data in
dicated a highly significant correlation between incidence of decay and skin (hypodermis) thickness. Although the correlation was high, it explained only 64% of the observed resistance to infection. Examination of berry attachment to the pedicel indicated that the angle formed between the fruit and the pedicel was correlated with resistance. A sharp angle, which enables spore accumulation and a suitable microclimate, was conducive to fungal development, whereas an obtuse angle did not allow such conditions to occur, and the berry remained healthy following artificial inoculation with R. stolonifer. Cultivar and temporal differences in tannin content correlated well with disease resistance, as did similar differences in the potential for phytoalexin production.