Luiz Carlos C. B. Ferraz

Host status of green manures for two isolates of Pratylenchus brachyurus in Brazil

Due to the complexity of management of plant-parasitic nematodes in cash crops, the use of non-chemical methods, such as rotation with green manures, has increased in recent years. However, data about the host status of green manures for lesion nematodes are scarce. Thus, two glasshouse trials were carried out to evaluate the host status of some green manures for two isolates of Pratylenchus brachyurus, a root-lesion nematode often found attacking soybean, maize and cotton in Brazil. Green manures tested were pigeon pea (Cajanus cajan) cultivars Fava Larga and Iapar 43, Crotalaria juncea, C. spectabilis, C. mucronata, C. breviflora, C. ochroleuca, C. paulina, velvetbean (Mucuna pruriens) cvs Black, Dwarf and Gray. Soybean cv. Pintado and French marigold (Tagetes patula) were included as standard good and poor hosts for P. brachyurus. In a separate glasshouse experiment, a naturally infested soil was used to evaluate the suitability of two green manures to P. brachyurus in comparison with two gramineaceous cover crops. In addition, morphometric studies were carried out with the two isolates of P. brachyurus used in experiments in order to confirm the species. Among the 11 green manures tested, at least two, C. spectabilis and C. breviflora, can be useful as rotation crops to reduce population densities of P. brachyurus, irrespective of the origin of the nematode. By contrast, all velvetbean cultivars and C. juncea must be avoided in infested areas as they are good hosts for the nematode.

Uptake and translocation of nitrogen, phosphorus and calcium in soybean infected with Meloidogyne incognita and M. javanica

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.

Effect of population densities of Heterodera glycines race 3 on leaf area, photosynthesis and yield of soybean

The effect of Heterodera glycines on photosynthesis, leaf area and yield of soybean (Glycine max) was studied in two experiments carried out under greenhouse condition. Soybean seeds were sown in 1.5 l (Experiment 1) or 5.0 l (Experiment 2) clay pots filled with a mixture of field soil + sand (1:1) sterilized with methyl bromide. Eight days after sowing, seedlings were thinned to one per pot, and one day later inoculated with 0; 1.200; 3.600; 10.800; 32.400 or 97.200 J2 juveniles of H. glycines. Experiment 1 was carried out during the first 45 days of the inoculation while Experiment 2 was conducted during the whole cycle of the crop. Measurements of photosynthetic rate, stomatic conductance, chlorophyll fluorescence, leaf color, leaf area, and chlorophyll leaf content were taken at ten-day intervals throughout the experiments. Data on fresh root weight, top dry weight, grain yield, number of eggs/gram of roots, and nematode reproduction factor were obtained at the end of the trials. Each treatment was replicated ten times. There was a marked reduction in both photosynthetic rate and chlorophyll content, as well as an evident yellowing of the leaves of the infected plants. Even at the lowest Pi, the effects of H. glycines on the top dry weight or grain yield were quite severe. Despite the parasitism, soybean yield was highly correlated with the integrated leaf area and, accordingly, the use of this parameter was suggested for the design of potential damage prediction models that include physiological aspects of nematode-diseased plants.

Molecular and morphometric analyses of Xiphidorus species (Nematoda: Longidoridae)

Xiphidorus nematodes are indigenous to Latin America and have a restricted geographical distribution compared to Xiphinema. A principal component analysis (PCA) based on eight morphometric characters from 39 South American populations clearly separated populations previously identified as X. achalae, X. amazonensis, X. minor, X. saladillensis and X. uruguayensis and three undescribed Xiphidorus species. However, populations identified as X. balcarceanus, X. parthenus and X. yepesara did not form similar discrete groupings and exhibited either considerable morphological variability or were incorrectly identified. Maximum likelihood phylogenetic trees derived from both 18S rDNA and ITS-1 sequences discriminated six Xiphidorus species (X. balcarceanus, X. minor, X. parthenus, X. yepesara, and two undescribed Xiphidorus species) from Brazil. Also, restriction analysis of PCR products derived from the ITS-1 region using three restriction enzymes (Taq I, Rsa I and Hin f I) yielded repeatable patterns that clearly discriminated these six Xiphidorus species. Sequence divergence was noted between X. parthenus and X. yepesara. Our morphometric and molecular data suggests that X. parthenus and X. yepesara are distinct species contrary to their previous subspecific status.

Confirmation of the synonymy of Paratrichodorus christiei (Allen, 1957) Siddiqi, 1974 with P. minor (Colbran, 1956) Siddiqi, 1974 (Nematoda: Triplonchida) based on sequence data obtained for the ribosomal DNA 18S gene

Sequence data were obtained for the full length of the ribosomal DNA (rDNA) 18S gene of specimens from three populations of Paratrichodorus christiei from the USA and four populations of P. minor from Brazil and Portugal. Alignment of the sequences and their application in a phylogenetic analysis revealed that the populations of P.christiei and P.minor formed a single cluster that differentiated from a second cluster comprising P.anemones and P.pachydermus. Previously, P.christiei had been proposed as a junior synonym of P.minor, but this synonymy had not been universally accepted, with many reports, particularly from the USA, continuing to refer to P. christiei. The results obtained here with the sequences of the rDNA 18S gene from the various populations confirm the validity of the synonymy of P.christiei with P.minor.

Characterization of Brazilian populations of Pratylenchus brachyurus using morphological and molecular analyses

In Brazil, Pratylenchus brachyurus damages economic important crops and it is managed with non-chemical methods such as crop rotation or resistant cultivars. However, the variability in reproduction and damaging effects observed among P. brachyurus populations could limit the efficacy and long lasting effect of nematode control practices. Twelve populations of P. brachyurus from different geographical areas of Brazil were analyzed morphologically and molecularly. The morphological and morphometric characters of the populations studied were variable, but fitted those of P. brachyurus. Assemblages of populations with different host preferences and reproductive capabilities were revealed by PCA of these populations using selected morphological characters. Phylogenetic analysis using ITS-rDNA sequences distinguished statistically supported groups of sequences that matched those of other populations of P. brachyurus deposited in the GenBank, confirming the identity of populations here studied. Intraspecific sequence diversity was observed among the populations. These variant sequences suggest the presence of microheterogeneity between ITS-1 copies in individuals. The findings of this study did not provide evidence of cryptic species in the P. brachyurus populations studied. The variability within and among populations of P. brachyurus observed in this work must be taken into consideration in breeding programs for resistance to this nematode.

Management of Pests and Nematodes

The number of insects that occur in sugarcane varies according to the plant’s phenology and region, with some insects being able to develop populations that result in considerable damage to producers. The concept of “pest” is economical, dynamic and depends on a series of factors: ecological (population level and season occurrence); economical (economic value of the culture, control objectives and costs); social (region development and historical moment); cultural (technical level of the producer); and mainly the interaction among these factors. Thus, insect population control strategies must be rather dynamic in order to comply with the utilization of different options, according to current interests. This chapter discusses the most relevant insects to sugarcane and their control.

Evaluation of damage caused on Coffea arabica by a population of Pratylenchus coffeae considered non-pathogenic on coffee

Two greenhouse experiments were carried out in order to evaluate the damage caused on Arabica coffee (Coffea arabica) by an M2 population of Pratylenchus coffeae, apparently non-pathogenic to coffee. Experiment 1, with Catuai Vermelho coffee at stage of two leaf pairs and with the initial nematode densities (Pi) of 0; 333; 1,000; 3.000; and 9,000 per plant, demonstrated that M2 can damage young coffee plants, although it is unable to reproduce on coffee roots. Experiment 2, with the same coffee cultivar and nematode densities, but with plants at stage of six leaf pairs, showed that the M2 population was unable to cause damage. Therefore, it was established that M2 is a population of P. coffeae without reproduction on Arabica coffee, which causes damage only in the first generation on young coffee below stages of six leaf pairs.