New Zealand Journal of Crop and Horticultural Science abstracts
Rind distortion of lemon caused by Botrytis cinerea Pers.
R. A. FULLERTON
F. M. HARRIS
I. C. HALLETT
The Horticulture and Food Research
Institute of New Zealand Ltd
Private Bag 92 169
Auckland, New Zealand.
email: rfullerton@hort.cri.nz
Abstract The infection process by
Botrytis cinerea
Pers. on lemon fruits (
Citrus limon (L.) Burm.), and development of rind
distortion are described. Infections occur on juvenile fruitlets soon after
petal fall from hyphae growing over the surface of the fruit from adjacent
colonised flower debris. The hyphae form compact infection cushions at their
tips. There is a collapse of epidermal cells and several layers of underlying
cells in the vicinity of the infection cushion, leading to the formation of
small necrotic pits on the surface of the fruit. As the fruitlets grow, there
is generalised hyperplasia in a zone up to 20 cell layers deep in the region of
the necrotic pits, leading to conspicuous outgrowths on the fruit surface. The
initial wound becomes stretched, flattened, and corky as the fruit enlarges. A
cambial layer is located below the area of damaged tissue, fluorescence in the
vicinity of the cork cambium indicates the presence of suberin in the cambium.
There was no evidence of suberin or lignin deposition in the region of the
original necrotic pit. The necrotic pits are characteristic of a non-pathogenic
reaction between the fungus and the host, with fungal hyphae failing to become
established in the necrotic tissues of the pit. The hyperplasia leading to the
rind distortions is considered to be a generalised reaction to the initial
wound and is commonly observed in lemon following other types of injury to the
rind. The principal sources of inoculum in orchards are
Botrytis-colonised floral debris caught up in flower clusters or
adhering directly to the fruit surface. The etiology of the disorder helps
explain why control by conventional fungicides is seldom successful. Not only
are there physical limitations to providing a protective cover on very small
fruit, but also the extended period over which flowering occurs in lemon
imposes limits on the number of applications able to be economically applied.
In the absence of effective control systems, growers are advised to modify
husbandry practices such as lowering the density of shelter belts, opening
lemon canopies to assist drying out of the flowers, and use of air blast
orchard sprayers to physically remove floral debris from the vicinity of young
fruit.
Keywords Botrytis cinerea; lemon; rind distortion;
infection; control
H99009
Received 22 February 1999; accepted 27 July 1999
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