Virus, Fertilizer and Rootstock Effects on the Growth and Precocity of Young Apple Trees

Abstract

SummaryThe growth and precocity of young apple trees on three clonal rootstocks, with four different latent virus infections, were compared on plots that had received different N P and K treatments for 40 years.Potassium deficiency severely reduced tree diameter, length of lateral shoots on 1-year-old trees and scion weight, without inducing leaf symptoms. The omission of nitrogen reduced growth less severely, but flower and fruit production were more severely affected.Latent viruses had less effect on growth and were slower to reduce tree weight and diameter than treatments deficient in potassium. All the virus inoculations reduced growth but the precocity was not always affected.MM.104, the strongest rootstock, increased growth and delayed flower production most, irrespective of virus or fertilizer treatments. Nevertheless MM.104 was also the most virus-sensitive; MM.lll was less so and MM.106 was relatively tolerant.Interactions occurred between virus and fertilizer treatments; when potassium was omitted the trees were small and consequently the viruses had least effect. The results suggest that a reduction in K fertilizer will be possible when virus-free trees are used.