Reaction of Psidium Accessions to the Meloidogyne enterolobii Root-Knot Nematode

The presence of the root-knot nematode, Meloidogyne enterolobii, in guava commercial orchards in many Brazilian states has caused severe loss to growers. 146 guava and aracazeiro (wild guava) accessions were evaluated in a greenhouse and nursery in order to find resistant accessions to be used as rootstock for commercial guava cultivars. In the greenhouse, 15 to 20 cm tall plants were inoculated with 10,000 nematode eggs, in a randomized complete design with an unequal number of replications. Under field nursery conditions, after seed germination, the plants were transferred to plastic bags with nematode contaminated soil. Five months after inoculation, the greenhouse accessions were evaluated for nematode damage. The nematode reproduction factor (RF) was estimated and the accessions classified as resistant or susceptible. The plants grown in the field nursery were visually evaluated for the presence of root galls one year after transplanting to plastic bags. A total of 66 Psidium, including 14 aracazeiro and 52 guava accessions, were evaluated under field nursery conditions. Two aracazeiros were classified as resistant, and another segregated for nematode tolerance under nursery conditions. All the guava accessions were susceptible in both evaluation conditions. Among the 20 aracazeiro accessions evaluated in the greenhouse, three were resistant to the nematode (RF<1) and 9, collected in the state of Rio Grande do Sul, were immune (RF=0). After further investigation performed among some resistant aracazeiro accessions collected in southern Brazil, sub-tropical region, poor plant development was observed in the northeastern Brazilian semi-arid region and low grafting compatibility with commercial guava cultivars. The current strategy to overcome this guava pest includes developing interspecific Psidium hybrids among resistant aracazeiros and susceptible guava to obtain hybrids with adequate plant height and stem diameter, highly compatible when used as rootstock for commercial guava cultivars.