Identification and characterization of a tomato introgression line with reduced wilting under drought

Abstract

Population growth and climate change pose a serious challenge to food supply. Agriculture is the biggest consumer of freshwater in the world. With widespread water scarcity and expected changes in rainfall patterns, both boosting plant yield using the same amount of water and increasing the survival and yield of crops under drought are top priorites for plant biologists. The understanding of genetic and physiological mechanisms controlling water-use efficiency (WUE) and of plant resistance to drought is, however, still limited. Tomato (Solanum lycopersicum L.) is an excellent genetic model with a rich source of natural variation in its wild relatives. S. pennellii Correll, among them, is adapted to the arid conditions of the Andean region in South America and exhibits a high tolerance to drought and increased WUE, measured as biomass gained per unit of water lost. In this work, a series of crosses and screening steps were done with the aim of introducing some of the genetic determinant(s) of S. pennellii‘s adaptation to drought into cultivated tomato (miniature cultivar Micro-Tom). Selecting hybrids with delayed wilting, a homozygous line was found which showed delayed wilting upon water deprivation and increased WUE. This novel genotype, named WELL (an acronym for Water Economy Locus in Lycopersicon) exhibited pleiotropic traits, including semi-determinate growth habit, elongated internodes, and more erect, wrinkled leaves. The introgressed segment was mapped to a pericentromeric region of 42 to 54 cM on the long arm of chromosome 1, which comprises the yellow fruit epidermis pigmentation gene. Physiological analyses showed that WELL leaves have lower stomatal conductance than their Micro-Tom counterparts under drought, in spite of a similar or slightly increased stomatal density, implying more closed stomata i.e. an increased stomatal sensitivity to water deprivation in WELL leaves. Recombinant lines with reduced introgressions (1-24 cM) were generated. Their preliminary analysis indicated that some of the pleiotropic traits in WELL were not genetically linked to the delayed wilting phenotype and two of the recombinant lines appeared to have altered growth responses under drought, but this deserves closer examination. Show more