Meloidogyne mayaguensis has been reported in some states of Brazil causing severe damage on commercial guava (Psidium guajava L.). Accessions of Psidium spp. were selected from a collection maintained in Embrapa Clima Temperado (Pelotas, Rio Grande do Sul State). Plants of different accessions were grown from seed in plastic bags and, when they reached 15-20 cm in height, were inoculated with 10,000 eggs/plant of M. mayaguensis. Eight months after inoculation, the different accessions were evaluated for resistance to M. mayaguensis. Three accessions of P. guajava were highly susceptible (RF=59.2) to this nematode. Psidium friedrichsthalianium was considered to be moderately resistant (RF=1.9). Three accessions of P. cattleyanum were immune to M. mayaguensis (RF = 0). When used as rootstocks P. cattleyanum and P. friedrichsthalianium were compatible with P. guajava cv. Paluma. Considering these results, the use of resistant rootstocks provides a promising control method for M. mayaguensis in commercial guava crop.

Two soybean (Glycine max) cultivars were used in this study, Ocepar 4, rated as moderately resistant to Meloidogyne incognita race 3 but susceptible to M. javanica, and 'BR 16', susceptible to both nematodes. The effect of nematodes infection on the uptake and transport of N, P and Ca to the shoot was studied in plants growing in a split root system. The upper half was inoculated with 0, 3,000, 9,000 or 27,000 eggs/plant while the lower half received 15N, 32P or 45Ca. Infected plants showed an increase of root but a decrease of shoot mass with increasing inoculum levels. In general, total endogenous nutrients increased in the roots and tended to decrease in the shoots with increasing inoculum levels. When concentrations were calculated, there was an increase in the three nutrients in the roots, and an increase of Ca but no significant variation of N and P was observed in the shoots. The total amount of 15N in the roots increased at the highest inoculum levels but 32P and 45Ca decreased. In the shoots there was a reduction of 32P and 45Ca. The specific concentrations of the labelled nutrients (abundance or radioactivity/tissue mass) also showed a decrease of 32P and 45Ca in the shoots and roots of infected plants and an increase of 15N in the shoots. Considering that overall nutrient concentrations reflect cumulative nutrient uptake and the data from labelled elements gave information at a specific moment of the infection, thus nematodes do interfere with nutrient uptake and translocation.

The worst nematode problem affecting guava is that created by root-knot nematode, which is a recognized limiting factor in commercial guava production in Central and South America. Considering the difficulty of identifying Meloidogyne enterolobii (=M. mayaguensis) only by the perineal pattern, this species has been misidentified in different regions around the world and identified frequently as M. incognita or Meloidogyne spp. The species' identification is possible using esterase phenotype and molecular markers. Using these techniques, only M. enterolobii was detected on guava in Brazil, confirming the incorrect identification. The intraspecific genetic variability of 16 M. enterolobii isolates from different geographical regions and hosts were analysed with different neutral molecular markers (RAPD, ISSR and AFLP) and showed a high level of homogeneity among the populations. Considering the low variability among M. enterolobii isolates, genetic resistance could be considered the most effective method of control, but only one accession of P. friedrichstalianium (Costa Rican wild guava) was resistant and compatible as rootstock with P. guajava 'Paluma', in field conditions. Although this root-knot nematode displays a very wide host range, studies showed that crop rotation is possible for cleaning areas infested with the nematode, using 35 antagonistic plants. Some cultivars of corn are also very promising for use in reducing populations of M. enterolobii in infested fields. Fourteen fruit trees are nonhost to M. enterolobii and only four fruit trees are good hosts. Considering the impossibility of cultivating guava in fields infested by M. enterolobii, crops presented as non-hosts or poor hosts could be used by the growers, but more studies should be done in the field, in infested areas, to support the results obtained in greenhouse conditions.

Two greenhouse experiments were carried out to characterize the resistance or susceptibility reactions of 52 species of plants to Meloidogyne ethiopica and their possible adverse effect on nematode population under greenhouse conditions. Tested plants with Reproduction Factor less than one (RF<1.0) were rated as non-hosts or resistant, including: peanut (Arachis hypogaea) 'Cavalo Vermelho', forage pigeon peas (Cajanus cajan) 'IAPAR 43'and 'PPI 832', Crotalaria grantiana, C. apioclice, C. spectabilis, dwarf velvet bean (Mucuna deeringiana), castor bean (Ricinus communis) 'IAC 80', sorghum (Sorghum bicolor) 'SARA', cowpea (Vigna unguiculata) 'Espace 10' and 'Australian', black oat (Avena strigosa) 'IAPAR' 61', ryegrass (Lolium multiflorum) 'Italian', forage radish (Raphanus sativus var. oleiferus) IPR116' and rye (Secale cereale) 'IPR 69'. The first 11 are summer plants and the last four winter plants. The other 37 species/cultivars tested were good hosts or susceptible. Some crop succession systems alternating summer and winter non-host plants are suggested for field experiments to validate these greenhouse results.

The identification of plant proteins expressed in response to phytopathogens is a remaining challenge to proteome methodology. Proteomic methods, such as electrophoresis and mass spectrometry have been extensively used for protein differential expression studies in several plants including Arabidopsis thaliana, rice, and wheat. However, in coffee (Coffea canephora) and cotton (Gossypium hirsutum), bidimensional electrophoresis (2-DE) analysis has been rarely employed. Moreover, global protein expression in both agricultural plants in response to biotic stress conditions had not been reported until now. In this study, Meloidogyne paranaensis and M. incognita, two devastating phytonematodes for numerous crop cultures, were used to infect resistant genotypes of coffee and cotton plants. The protein expression of infected- and non-infected roots were evaluated by 2-DE following in silico experiments. Additionally, gels were stained with silver nitrate and/or Coomassie brilliant blue in order to obtain an optimized method for proteomic analysis of plant-nematode interaction. The 2-DE analysis revealed an enhanced number of protein spots, as well as differentially expressed proteins, when Coomassie brilliant blue was used. The results obtained here could be extended to other plant species, providing valuable information to root-nematode interactions.

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