STUDIES ON THE PHYSIOLOGY AND PARASITISM OF BOTRYTIS CINE RE A PERS

Abstract

Summary Culture studies were made with varieties B 1c and B 12c of Botrytis cinerea in which nitrogen was supplied in different combinations. From these studies it became evident that no definite conclusion may be drawn as to whether any of these two varieties prefer nitrogen in the ammonium or in the nitrate form. Though the growth of these fungi was usually somewhat poorer on the media in which nitrogen was available in the nitrate form, the greatest weight of mycelium was produced per unit weight of consumed nitrogen from this source. The amount of acid produced per unit weight of consumed nitrogen was greater on media containing ammonium or nitrates which were less favourable to growth. The hydrogen‐ion concentration of the medium, originally standardized at pH. 6.0, and the total amount of acid of this medium was increased by both varieties of B. cinerea. The increase in hydrogen‐ion concentration was greater where nitrogen was supplied in the ammonium form than where it was supplied in the nitrate form. Both varieties acidified all sets of media containing ammonium nitrate as a source of nitrogen, whether the initial hydrogen‐ion concentration was pH 8.6 or 2.7. The sets of media, in which nitrogen was supplied in the form of sodium nitrate, were acidified when their initial hydrogen‐ion concentration was pH. 7.4. Where this concentration was pH 2.6, it was however decreased to pH 5.2 by culture B 1c, while the total amount of acid in these sets of media was still increased. Culture B 12c not only decreased the hydrogen‐ion concentration of this medium, originally at pH 2.6, but also its total amount of acid. Uninjured Henab Turki grapes in different stages of maturity showed an increasing susceptibility to infection by B 12c with advance of maturity. Injured berries of this variety were slightly susceptible to invasion by this fungus even when they were green. Inoculation results of raw, sterile juice from representative samples of these grapes with culture B 12c show that a fair amount of growth occurred even on juice from the greenest grapes experimented with. The important role played by the cuticle and cell walls in the protection of grape berries against penetration and invasion respectively by B. cinerea was clearly demonstrated in this experiment. The hydrogen‐ion concentration and the total amount of acid of grape juice of pH. 3.0 at the time of inoculation was increased by culture B 12c. Where the hydrogen‐ion concentration of the juice was originally below pH. 3.0, this concentration, as well as the total amount of acid, was decreased by this fungus. The changes in the acid reactions of media by B. cinerea are, therefore, dependent upon (a) the variety of this fungus, (b) the initial hydrogen‐ion concentration of the substrate, and (c) the source of nitrogen supplied.