Bypassing of a polygenic Microcyclus ulei resistance in rubber tree, analyzed by QTL detection

Abstract

Research Summary• Genetic resistance components of the Hevea brasiliensis × H. benthamiana RO 38 cultivar to Microcyclus ulei disease were investigated by inoculating isolates which succeeded in partially or completely infecting genotypes of a mapping population.• Progeny of a cross between RO 38 and a susceptible cultivar was inoculated under controlled conditions with three isolates and scored for two resistance traits. Interval mapping and a nonparametric test were used to detect resistance quantitative trait loci (QTLs).• Eight significant QTLs were detected, all of them inherited from the interspecific parent. Among these QTLs, only one contributed to the partial resistance against a highly pathogenic isolate, and no QTL was detected for resistance against the most pathogenic isolate. As an unexpected result, a single isolate can thus completely bypass this polygenic resistance.• This complex situation, where no clear relationship can be established between number of resistance factors and qualitative vs quantitative or partial vs complete resistance, is discussed and suggestions as to the detection of new and sustainable resistance sources are proposed.

A rubber tree’s durable resistance to Microcyclus ulei is conferred by a qualitative gene and a major quantitative resistance factor

“…After many studies that attempted to define parameters that could give a good description of the disease (Chee et al 1985;Junqueira et al 1990) and others describing the diversity of M. ulei strains Hashim and Almeida 1987;Junqueira et al 1986;Mattos et al 2003), the first identification of the genetic factors that could confer resistance to SALB was carried out in an interspecific hybrid (H. brasiliensis × Hevea benthamiana; Lespinasse et al 2000a). Important resistance QTLs and a major resistance gene Lespinasse et al 2000a) were described, but a further study on the same material showed that this resistance has already been bypassed by some highly pathogenic M. ulei isolates (Le Guen et al 2007). Recently, a new and apparently durable resistance to SALB was identified in the H. brasiliensis cultivar MDF 180 (Le Guen et al 2008).…”

In vitro plant regeneration from ovules of Taraxacum officinale and Taraxacum koksaghyz

“…In 1934, Microcyclus ulei, the cause of South American Leaf Blight (SALB) on rubber trees, wiped-out *Corresponding author. E-mail: traud.winkelmann@zier.uni-hannover.de rubber plantations in Southeast Asia and Brazil on a large-scale (Le Guen et al, 2007). However, due to economic reasons, rubber plantations were replaced by oil palm plantations in numerous countries, especially in Malaysia, because labor costs for the laborious latex harvesting were high and the economy of these countries was shifting to an industrial base.…”

Production of renewable polymers from crop plants

“…The rubber tree used in commercial production in South-East Asia has a very narrow genetic basis, coming essentially from a few seeds collected at one location in Brazil by Dr Henry Wickham in 1876 (Polhamus, 1962). It is very sensitive to the pathogen Microcyclus ulei, the causative agent of South American leaf blight (Le Guen et al, 2007). South American leaf blight has essentially ended large-scale Hevea rubber production in South America, and can be expected to have a similar devastating effect if it spreads to Asia (Davis, 1997).…”