Inge Van den Bergh

Responses of Vietnamese Musa genotypes to Meloidogyne spp. under field conditions

Eight Vietnamese Musa genotypes, belonging to the AA, AAA, ABB and BB genome groups, as well as FHIA-01 (AAAB), FHIA-02 (AAAA) and Yangambi Km 5 (AAA) were evaluated for their host-plant response to Meloidogyne spp. under field conditions. FHIA-01, Ngu Thoc (AA), Tay (ABB) and Com Lua (AAA) were found to be less susceptible to Meloidogyne spp. FHIA-01, Ben Tre (AAA) and Bom (AAA) were less sensitive to knot-forming activity of Meloidogyne spp. The population dynamics of the nematodes were also assessed. The number of juveniles recovered from the roots was strongly influenced by the weather. During the cool dry season, the numbers dropped drastically. The number of egg-laying females in the roots was much less influenced by environmental conditions. Their numbers did not increase during the cooler and dry season. No effects of the nematodes on plant growth were found. The number of nematodes in the roots was related to the physiological stage of the plants, with most nematodes present during flowering.

The need for culture collections to support plant pathogen diagnostic networks.

Plant-pathogenic microorganisms, by virtue of their size, similarity in disease symptoms and closely related morphologies, are notoriously difficult to diagnose and detect. Diagnosis gives proof as to the causal agent of disease and is important for developing appropriate control measures. Detection shows the presence of a microorganism and is of importance for safeguarding national and international trade. Live reference collections are required to characterize the taxonomy and function of microorganisms as a prerequisite to development of tools for diagnosis and detection. Two case studies will be presented in this paper to demonstrate the importance of microorganism collections for facilitating knowledge sharing and the development of identification methods. Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense and sharka disease of stone fruits caused by plum pox virus (PPV) are considered. Both diseases consist of different races/strains with different host specificities, but Fusarium wilt poses a threat to food security, while PPV poses a threat to trade due to its classification as a quarantine pest, since there is no anti-virus treatment available to control sharka disease in orchards. It is only through comprehensive collections of correctly identified and well-maintained strains representing the genetic diversity of a target organism that robust, specific, reliable and efficient diagnostic and detection tools can be developed.

Influence of Pratylenchus coffeae and Meloidogyne spp. on plant growth and yield of banana (Musa spp.) in Vietnam

The objective of the presented study was to look at the effect of Pratylenchus coffeae and Meloidogyne spp., the two major nematode species associated with banana ( Musa spp.) in North Vietnam, on the plant growth and yield of cv. Grand Naine (AAA) and four local banana cultivars, Ngu Tien (AA), Hot (BB), Ben Tre (AAA) and Tay Tia (ABB). Inoculated plants were compared with nematode-free control plants in terms of plant growth, crop cycle duration and yield under field conditions in Hanoi, North Vietnam. Infection with P. coffeae did not affect the crop cycle duration or the plant height, the pseudostem girth or the number of standing leaves at harvest of any of the cultivars, but did significantly reduce the bunch weight of cv. Ngu Tien from 6.6 to 5.3 kg (20% reduction), the bunch weight of cv. Tay Tia from 7.3 to 5.9 kg (19% reduction) and the bunch weight of cv. Grand Naine from 6.9 to 6.0 kg (13% reduction). The bunch weight of cvs Hot and Ben Tre was not significantly affected. The number of hands of the inoculated and the control plants did not differ for any of the cultivars but infection with P. coffeae resulted in a 34% reduction in the number of fingers of cv. Grand Naine (from 67 to 44 fingers). The number of fingers of the other cultivars were not affected by inoculation with P. coffeae. Infection with Meloidogyne spp. did not affect the time from planting to harvest for any of the cultivars, but the time from planting to shooting was increased from 367 to 387 days for cv. Ngu Tien. The plant height and the pseudostem girth at harvest of cv. Grand Naine were significantly reduced by 27% and 18%, respectively. The number of standing leaves as well as the plant height and the pseudostem girth at harvest of the other cultivars were unaffected. Infection with Meloidogyne spp. significantly reduced the bunch weight of cv. Ngu Tien from 6.6 to 5.1 kg (23% reduction) and the bunch weight of cv. Grand Naine from 6.9 to 5.6 kg (19% reduction). The bunch weight of cv. Hot was unaffected. Infection with Meloidogyne spp. reduced the number of hands of cv. Ngu Tien by 14% (from 6.2 to 5.4 hands) the number of fingers of cv. Grand Naine by 25% (from 67 to 50 fingers). The number of hands and fingers of the other cultivars were not affected. The results indicate that in areas where the burrowing nematode, Radopholus similis, is not present, other nematodes, especially Meloidogyne spp., may become more important in terms of damage and yield loss.

Population dynamics of Pratylenchus coffeae on banana in North Vietnam

The reproductive fitness of a Pratylenchus coffeae population, collected from banana roots in North Vietnam, was studied in relation to temperature and moisture under screenhouse and field conditions. In the screenhouse, the population grew much more slowly during the cooler winter months than during the summer and an excess of soil moisture reduced the nematode population drastically. The results were confirmed in the field. The nematode population in the roots of the banana plants initially increased over time but was reduced during the cooler winter months and remained nearly constant during the wettest months when the field was almost continuously flooded. These observations may explain why P. coffeae populations on Musa do not increase to dramatic levels in North Vietnam, with its cool winter temperatures and periods of abundant rainfall during several months of the year.

Yield response of four popular banana varieties from Southeast Asia to infection with a population of Radopholus similis from Davao, Philippines

The yield response of four popular banana cultivars from southeast Asia to infection with a population of Radopholus similis collected from banana in Davao, Philippines, was investigated in a microplot experiment. Bunch weight reduction of nematode-infected plants ranged from 25 to 68% for all four southeast Asian banana cultivars and Grand Nain (AAA), the susceptible reference cultivar included in the study. The banana cv. Latundan (AAB) had a nematode population density of 185, 38 and 27 nematodes at 6 months after planting, flowering and harvesting, respectively, and a low bunch weight reduction (25%) compared with the other banana cultivars examined, possibly suggesting that this cultivar is partially resistant to R. similis.