Susceptibility of Flordaguard peach rootstock to a resistant-breaking population of Meloidogyne floridensis and two populations of Meloidogyne arenaria.

Sai Qiu,Thomas G Beckman,Mary Ann D Maquilan,Donald W Dickson,Jose X Chaparro,Janete A Brito

doi:10.21307/jofnem-2021-111

Abstract

Cultivar Flordaguard is suggested as a root-knot nematode (RKN) resistant rootstock for Florida peaches, however, RKN disease has been observed on this rootstock in peach orchards. Our goal was to confirm whether the RKN resistance breaking isolates of M. floridensis and M. arenaria indeed could infect and reproduce on the peach rootstock cv. Flordaguard in both laboratory and field studies. Root galling occurred on all peach cultivars evaluated including Flordaguard, Flordaglo, Okinawa, and Lovell, in the presence of the RKN resistance-breaking isolates of M. floridensis (MfGnv14) and two M. arenaria isolates (Ma1 and Ma2). These rootstocks showed varying degrees of susceptibility (to a lesser extent in Okinawa) to these three RKN resistance-breaking isolates. The importance of nematode inoculum concentrations in differentiating between resistance and susceptible plants was demonstrated, and thus are an important factor to consider in nematode resistance breeding programs. In host differential tests the peach-originated isolates of M. floridensis and M. arenaria behaved similarly with the vegetable-originated isolates of M. floridensis on tomato, peanut, watermelon, and tobacco, but showed variable host responses on cotton and pepper. The two M. arenaria isolates from peach reproduced on pepper but not on peanut. To our knowledge this is the first report of M. arenaria race 3 infecting Flordaguard and pepper in Florida. Soil and root samples collected from cv. Flordaguard infected trees at two commercial peach orchards showed that M. floridensis and M. arenaria were established on the rootstock.

Highlights

That could have happened in some orchards but in two commercial orchards where trees were infected by M. floridensis and M. arenaria numerous trees had the characteristic red-leaf stems growing off the rootstock, which suggested the rootstock was true to variety
Our objectives were to: (i) determine infectivity and reproduction on root-knot nematode (RKN) resistant and susceptible peach rootstock cultivars at different inoculum levels of a resistance-breaking M. floridensis isolate; (ii) determine the infectivity of M. floridensis and M. arenaria isolates to three peach rootstock cultivars; (iii) confirm the sus ceptibility of the resistant Flordaguard rootstock to the resistance-breaking nematode isolate, M. floridensis, and the two M. arenaria isolates; iv) conduct differential host tests of four M. floridensis and three M. arenaria isolates; and v) confirm infection of Flordaguard rootstock by M. floridensis and M. arenaria populations in two commercial peach orchards
These three isolates failed to induce galls and did not reproduce on the RKN resistant Flordaguard, in contrast to the heavy infection induced by the RKN resistance breaking isolate MfGnv14 (Table 2)

Summary

Introduction

Okinawa and Nemaguard were planted extensively in Florida during the 1960’s because they were considered to have a high degree of resistance to the prevalent RKN species M. incognita and M. javanica (Sherman and Lyrene, 1983). These root stocks, including Nemared, were eventually found to be susceptible to a RKN population in North Florida. Flordaguard was reported as resistance to all Meloidogyne spp. considered a threat to the peach industry in Florida and was suggested to become the standard rootstock for commercial low-chill peach production replacing Okinawa and Nemaguard (Sherman et al, 1991). Our objectives were to: (i) determine infectivity and reproduction on RKN resistant and susceptible peach rootstock cultivars at different inoculum levels of a resistance-breaking M. floridensis isolate; (ii) determine the infectivity of M. floridensis and M. arenaria isolates to three peach rootstock cultivars; (iii) confirm the sus ceptibility of the resistant Flordaguard rootstock to the resistance-breaking nematode isolate, M. floridensis, and the two M. arenaria isolates; iv) conduct differential host tests of four M. floridensis and three M. arenaria isolates; and v) confirm infection of Flordaguard rootstock by M. floridensis and M. arenaria populations in two commercial peach orchards

Objectives

Methods

Results

Conclusion