Vanessa S. Mattos

Genetic diversity of Meloidogyne spp. parasitising potato in Brazil and aggressiveness of M. javanica populations on susceptible cultivars

Root-knot nematodes ( Meloidogyne spp.) significantly impact potato production worldwide and in Brazil they are considered one of the most important group of nematodes affecting potatoes. The objectives of this study were to survey Meloidogyne spp. associated with potatoes in Brazil, determine their genetic diversity and assess the aggressiveness of M. javanica on two susceptible potato cultivars. Fifty-seven root-knot nematode populations were identified using esterase phenotyping, including Meloidogyne javanica , M. incognita , M. arenaria and M. ethiopica . Overall, root-knot nematodes were present in ca 43% of sampled sites, in which M. javanica was the most prevalent species, and the phenotypes Est J3, J2a and J2 occurred in 91.2, 6.7 and 2.1% of the positive samples, respectively. Other species, such as M. incognita , M. arenaria and M. ethiopica , were found less frequently and occurred at rates of 6.4, 4.3 and 2.1% of the samples, respectively. Sometimes, M. javanica was found in mixtures with other root-knot nematodes in ca 10.6% of sites containing Meloidogyne . After confirming the identification of 17 isolates of M. javanica and one isolate each of M. incognita , M. arenaria and M. ethiopica by SCAR markers, the populations were used to infer their genetic diversity using RAPD markers. Results revealed low intraspecifc genetic diversity among isolates (13.9%) for M. javanica . Similarly, M. javanica sub-populations (J2a) clustered together (81% of bootstrap), indicating subtle variation from typical J3 populations. The aggressiveness of four populations of M. javanica from different Brazilian states on two susceptible potato cultivars was tested under glasshouse conditions. Results indicated differences in aggressiveness among these populations and showed that potato disease was proportional to nematode reproduction factor.

Genetic variability of Meloidogyne paranaensis populations and their aggressiveness to susceptible coffee genotypes.

Meloidogyne paranaensis is one of the most destructive root-knot nematode (RKN) species parasitizing coffee in Brazil and in the Americas generally. The objectives of this study were to assess the genetic variability, aggressiveness and virulence of seven different M. paranaensis populations on susceptible and resistant Coffea spp. All seven RKN populations were identified by biochemical and molecular methods. Coffee seedlings were inoculated in the greenhouse, and the nematode reproduction factor was used to infer their reproduction on coffee genotypes. Phylogenetic studies showed a low genetic variability in M. paranaensis populations, regardless of the existence of three esterase phenotypes (Est P1, P2 and P2a), except for the population Est P2a from Guatemala, which is genetically different from other M. paranaensis populations from Brazil. The Est P2a and Est P2 (Herculândia, SP, Brazil) populations were the most aggressive on two susceptible C. arabica cultivars under greenhouse conditions. None of the M. paranaensis populations was virulent on resistant coffee genotypes, confirming their resistance to the seven M. paranaensis populations tested. The resistant coffee cultivars, namely Clone 14 INCAPER, Catuai Vermelho x Amphillo MR2161 (E1 16-5 III), Apoata IAC 2258, Timor Hybrid UFV 408-01 (E1 6-6 II) and IPR 100, exhibited segregation for resistance in the ratio of 0%, 2.4%, 12%, 26% and 29%, respectively. These are promising results, because they validate resistance against several M. paranaensis populations in different Coffea spp. genetic resources, which can be used in breeding programs or as rootstocks, such as ‘Apoata IAC 2258’ and ‘Clone 14 INCAPER’. This article is protected by copyright. All rights reserved.