A search for tolerance to black root rot in strawberry.

摘要

Black root rot (BRR) is a widespread disease of strawberry ( Fragariaxananassa Duchnesne) that causes the death of feeder roots and the degradation of structural roots. The major causal organisms of black root rot include Rhizoctonia fragariae Husain and W.E. McKeen, Pythium Pringsh. spp. and Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is scheduled to be phased out in 2005, and its effects are short-lived in matted-row systems. The objectives of the first study were to measure levels of tolerance to black root rot in 20 strawberry genotypes and to determine which pathogens were present in the soil. The genotypes were planted in four blocks each of methyl-bromide fumigated and nonfumigated soil, and were evaluated for crown number, number of flowers per crown, yield, and average berry weight over two years. The results showed that all three pathogens were present in the field, and that there was a significant genotype x fumigation interaction for yield and crown number in both years. The cultivars Bounty, Cabot, and Cavendish, all released from the breeding program in Nova Scotia, displayed tolerance to the pathogens that cause BRR. The objective of the second study was to determine the heritability of BRR tolerance. Nine genotypes were chosen from the previous study to use as parents: three that displayed high tolerance to BRR ('Bounty', 'Cabot', and 'Cavendish'), three that displayed intermediate tolerance ('Guardian', 'Midway', and 'Winona'), and three that displayed little or no tolerance ('Jewel', LH50-4, and 'Mesabi'). The progeny from a diallel cross were grown on fumigated and nonfumigated soil and evaluated for crown number, flower number, and yield. Results showed no interaction between treatment and family, indicating that breeding for increased tolerance to BRR will be difficult.