Biological control of Botrytis cinerea on kiwifruit : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticulture Science at Massey University

Abstract

Screening for potential antagonists was carried out on plant parts of kiwifruit (Actinidia deliciosa var. delicisa [A.Chev]. Lang & Ferguson, cv. Hayward) taken from kiwifruit orchards in four collections. A range of microorganisms have shown potential activity against Botrytis cinerea Persoon. ex Fries, on Potato dextrose agar (PDA) petri dish at various temperatures, including 0°C. The antagonism was also tested on different media with different pH for antibiosis or mycoparasitism action. It was found that temperature had a much greater effect on growth and activity of the antagonists than did pH. Three isolates (FB3, FF9, FO30) which showed good biocontrol activity were tested for ability to inhibit spore germination and germ tube elongation of B.cinerea on 2.5% vegetable juices (V.8) medium discs. One of these isolates (FO30: Fusarium merismoides) showed such ability. These isolates were selected for a trial on kiwifruit. Stem end rot was partially controlled under storage condition when the pathogen (B.cinerea) and the antagonist were inoculated simultaneously. Harvested fruit were inoculated with different inoculum levels and subjected to different curing periods. The inoculum level of Fusarium merismoides isolate FO30 showed a significant affect on the percentage of soft rot caused by B.cinerea, and reduced disease incidence on kiwifruit by 17-21% after 13 weeks storage at 0°C. The curing period did not have any significant effect on the percentage of soft rot except when the fruit was cured for 2 days at ambient temperatures, inoculated, and left 2 further days at ambient temperatures before storage at 0°C. Further work is required to investigate enhancement of biocontrol of B.cinerea on kiwifruit by manipulation of the curing period. Several microscopic stains including Chlorazol black, Lactophenol cotton blue and phloxine gave good staining of the spores and mycelium of B.cinerea and antagonists on 5% V.8 medium and kiwifruit tissue.