Extreme resistance to potato virus Y (PVY) and its effect on tuber yield of some potato clones

A study to evaluate potato clones for extreme resistance to potato virus Y (PVY) and to estimate the effect of the virus on tuber yield was conducted under lowland conditions at Canlubang, Calamba, Laguna [Philippines]. A total of 212 potato clones derived from crosses involving parent with different genetic backgrounds were tested against PVY resistance under field condition for two seasons. Based on freedom of symptoms coupled with ELISA [Enzyme linked immunosorbent assay] 27 clones were selected, of which 15 were determined for their genetic constitution with respect to extreme resistance to PVY through test crosses. Possible genotypes are proposed and discussed. Yield loss from PVY was a function of varietal resistance/tolerance, disease severity and length of time from infection. Clones with either hypersensitivity or extreme resistance showed no reduction in the tuber yield. On the contrary tuber was adversely affected in susceptible clones. The clone B -71-240.2 appeared to be susceptible to PVY infection but tolerant to loss tuber yield. Lt-7, a clone with good ability to grow from cuttings under lowland conditions, was highly susceptible to the virus. The earlier the infection occurred the more severe the symptoms and consequently, the higher was the reduction in tuber yield. The relationship between loss in tuber yield and disease severity was fitted to a linear model. Based on this, an equation for estimating the loss in tuber yield was formulated. Based on path coefficient analysis, the virus induced loss in tuber yield was found to be due to reduction in both tuber number and average tuber weight, but the former appeared to be more important than the latter. In comparison with healthy plants, the compensatory effect between two tuber yield components was reduced in infected plants.