Effect of Inarched, Two-Rootstock Trees, on Development, Yield and Disease Resistance of 'Valencia' Orange

Susceptibility to sudden death, blight and foot rot diseases, and to nematodes, has not prevented Rangpur lime from still being the most used citrus rootstock in Brazil due to its drought resistance, adaptability to poor soils, and productivity. Historically, inarching trees on susceptible rootstocks with others resistant conferred tree resistance against root and trunk diseases. Experiments were established in 2005 and 2007 to compare 'Valencia' trees propagated on (1) Rangpur lime, (2) Swingle citrumelo, or (3) inarched using these two rootstocks. Inarched trees had the same height as those on Rangpur lime alone and both types were taller than trees on Swingle citrumelo alone in the 5th year of the orchard. Trees grafted on Swingle tended to yield less fruit than those grafted on Rangpur lime in the first 2 to 4 crops, while inarched trees tended to yield intermediate to larger crops. Fruit quality of inarched trees tended to be intermediate or similar to that of the best quality inducing rootstock. Swingle rootstock totally protected inarched trees from foot rot in the first 7 years of the orchard while trees on Rangpur alone had 1.5% to 2% disease incidence. Therefore, inarching can be used to take advantage of the complementary qualities of known rootstocks regarding disease resistance, tree height, productivity, and fruit quality.