Seedling Cultivation of Virus-Free and Common Lemon Varieties:Ⅰ.Plant Growth,Fruit Yield and Disease Susceptibility

Plant growth,fruit yield and disease susceptibility of the lemon trees from seedlings of selected virus-free and common varieties were monitored for 6years.It was found that the virus-free variety had higher crowns,by 1.9%to 17.75%,and the diameter of its graft-set interface 1.81%to 24.61%greater than the common variety.In the third year,the per hectare fruit yield of the virus-free lemon trees was higher than its counterpart,but the difference was not significant.However,the difference became significantly higher at 24.70% to 36.24% afterward.And,the common lemon variety showed a continuous decline on fruit yield in the 5th and 6th year.In addition,they were infected with exocortis and tristeza diseases in the second year.After the 3rd year,the infection rates of exocortis were 9.5%-30.3%,and tristeza 4.5%-14.0%.