Partial Resistance to Melampsora larici-populina Leaf Rust in Hybrid Poplars: Genetic Variability in Inoculated Excised Leaf Disk Bioassay and Relationship with Complete Resistance

Abstract

Inoculated excised leaf disk technique allows decomposition of poplar partial resistance to Melampsora larici-populina leaf rust into key epidemiological components such as latent period (LP), uredinia number (UN), uredinia size (US), and spore production (SP) for a given M. larici-populina strain under controlled environmental conditions. Three hundred thirty-six genotypes from an interspecific Populus deltoides x P. trichocarpa F(1) progeny segregating for complete resistance to M. larici-populina strain 93ID6 were inoculated with M. larici-populina strain 93CV1. This strain was able to infect the whole family, except few probable recombinants. LP, final UN, and final US after one infectious cycle proved to be relevant complementary descriptors of partial resistance. Area under the disease progress curve and other parameters of uredinia appearance dynamics did not yield additional information. Indirect assessment of SP by US scoring was reliable and easy to access compared with direct spore counting. UN was the only trait for which a doubling of the inoculum pressure level had a significant effect, leading to greater differentiation between genotypes. Consistent with previous studies is the clear relationship between presence of complete resistance against M. larici-populina strain 93ID6 and higher partial resistance to M. larici-populina strain 93CV1 (32% longer LP, 76% smaller UN, and 34% smaller US). In the subpopulation compatible with 93ID6, bimodal distribution of genotypic means for US suggested implication of a major gene inherited from the P. trichocarpa parent. Residual variation was noted for the three epidemiological components, suggesting that additional genes might condition these quantitative traits.

A standardised method for the quantitative analysis of resistance to grapevine powdery mildew

“…Automatic cell counters are powerful tools for measuring pathogen sporulation, highly suited to large sample sets like mapping populations (Dowkiw et al 2003;Bellin et al 2009;Blasi et al 2011). By comparing the results obtained using an automatic cell counter with those using a haemocytometer in a serial dilution we showed a good correlation between both methods (Fig.…”

Presence of defeated qualitative resistance genes frequently has major impact on quantitative resistance to Melampsora larici-populina leaf rust in P. × interamericana hybrid poplars

“…The inocula used for this study consisted of urediniospores from four single-uredinial M. larici-populina strains (i.e., 93JE3, 93CV1, 98AG69, and 98AR1) belonging to four different pathotypes (i.e., 2-3-4, 1-3-4-5, 1-3-4-5-7, and 1-3-4-5-7-8, respectively). Each inoculum was increased and stored as described by Dowkiw et al (2003).…”

“…Main advances include the observation of significant amounts of genetic variability for several quantitative resistance components in laboratory and field tests and the identification of underlying genetic factors through genetic mapping and quantitative trait loci (QTL) detection (Lefèvre et al 1994(Lefèvre et al , 1995(Lefèvre et al , 1998Goué-Mourier et al 1996;Villar et al 1996;Dowkiw et al 2003;Dowkiw and Bastien 2004;Jorge et al 2005).…”

Exploiting Natural Variation to Uncover an Alkene Biosynthetic Enzyme in Poplar

“…Inoculations were performed as described previously (Ward and Ostry, 2005;Dowkiw et al, 2003). For Septoria musiva, discs were inoculated with 10 5 spores/mL of strain 6-1 obtained from Indian Head, Saskatchewan.…”