Resistant accessions of wild Psidium spp. to Meloidogyne enterolobii and histological characterization of resistance.
Meloidogyne enterolobii has been reported in some states of Brazil and other countries causing severe damage on commercial guava (Psidium guajava). The use of resistant varieties is the most effective way to manage nematode parasitism. This study screened 51 accessions of Psidium spp. selected from the Psidium Germplasm Collection (Embrapa) to look for resistance against M. enterolobii. Six months after inoculation, nematode reproduction factor (RF) was used to assess resistance. The following species were resistant to M. enterolobii: P. cattleianum (yellow guava), P. friedrichsthalianum (Costa Rican guava), Acca sellowiana (feijoa) and P. rufum (purple guava). All 43 wild accessions of P. guajava were susceptible, as well as three accessions of P. guineense (Brazilian guava), one of P. acutangulum (pear guava) and the susceptible control P. guajava cv. Paluma. When used as rootstocks under greenhouse conditions, P. cattleianum and P. friedrichsthalianum were compatible with cv. Paluma; however, in greenhouse and field conditions only 50% of both scions survived. No apparent hypersensitive response (HR) was seen in the resistant guava P. cattleianum and P. friedrichsthalianum. Juveniles were able to develop normal feeding sites similar to those in susceptible roots 6-13 days after inoculation (dai). From 27 to 32 dai, giant cell deterioration was observed and nematodes showed arrested development. The majority of nematodes failed to reach maturity and did not begin laying eggs in resistant roots. These results suggested that the induction of resistance is relatively late in this pathosystem.