Genetic diversity analysis of avocado (Persea americana Miller) rootstocks selected under greenhouse conditions for tolerance to phytophthora root rot caused by Phytophthora cinnamomi

Abstract

Phytophthora cinnamomi, the causal agent of Phytophthora Root Rot (PRR) of avocado, is the most serious disease of avocado worldwide. The development of tolerant rootstocks to control PRR has proven to be an effective means to control the disease. However, using traditional breeding approaches can take over a decade to produce results and there has been a limited use to integrate molecular data into breeding efforts. Therefore, the objective of this work was to use amplified fragment length polymorphism (AFLP) to genetically characterize greenhouse selected PRR tolerant rootstocks, some that had been field-tested and others that had not. Sixty-one polymorphic markers were identified among the 83 cultivars/selections tested. Based on UPGMA analysis, extensive genotypic diversity was found with the closest genotypes differing by six markers. No obvious trends were observed based on the cluster analysis with regards to known tolerant and susceptible rootstocks but rootstocks that have been field-tested and determined to be very tolerant rootstocks such as Latas, Dusa, PP14 (Uzi), PP4 (Zentmyer), and PP24 (Steddom) were distributed across the tree. This suggests that the same mechanisms for resistance may not be shared among these various selections. Therefore, these best-performing and most genetically diverse rootstocks will be combined in future breeding efforts to potentially pyramid diverse sources of resistance into future selections.

Diversity of avocado (Persea americana Mill.) cultivars from Antioquia (Northeast Colombia) and comparison with a worldwide germplasm collection

“…The evaluation of their morphological characters is inaccurate due to the influence of environmental factors, subjectivity, and a limited number of discriminating traits (Alcaraz and Hormaza, 2007). Consequently, avocado characterization and diversity studies have been strengthened by analyses of genetic markers including isozymes (Torres and Bergh, 1978), minisatellites (Mhameed et al, 1997), random amplified polymorphic DNA (RAPD) (Fiedler et al, 1998), restriction fragment length polymorphism (RFLP) (Davis et al, 1998), single sequence repeats (SSRs) (Ashworth and Clegg, 2003;Schnell et al, 2003;Alcaraz and Hormaza, 2007;Kwame et al, 2008;Gross-German and Viruel, 2013), amplified fragment length polymorphism (AFLP) (Douhan et al, 2011;Cañas-Gutierrez et al, 2015), and single nucleotide polymorphism (SNP) (Chen et al, 2008).…”

EST sequencing and gene expression profiling of defence-related genes from Persea americana infected with Phytophthora cinnamomi

“…Their efficacy has yet to be tested for use in identifying tolerant rootstocks, but it is known that they amplify across all avocado varieties and can be used for investigation of genetic relations [ 34 , 35 ]. The University of California Riverside (UCR) has recently employed 61 polymorphic AFLP markers to characterise PRR tolerance in 83 rootstocks from various locations including South Africa and Israel with the majority of rootstocks from the UCR collection [ 36 ]. The study concluded that resistance mechanisms vary between tolerant cultivars and no trend was observed in the cluster analysis.…”

Parameters for the standardization of chlorophyll and assessment of PS II quantum efficiency for avocado (Persea americana Mill)

“…and Phytophthora cinnamomi Rands. are potentially limiting, being P. cinnamomi the most devastating oomycete in avocado commercial crops (GEORGE 1956, GABOR 1991, DOUHAN ET AL. 2011.…”