Roberto K. Kubo

Carbon Fixation and Partitioning in Coffee Seedlings Infested with Pratylenchuscoffeae

The objective was to study CO2 fixation and photoassimilate partition in coffee (Coffea arabica) seedlings infested with the lesion nematode Pratylenchus coffeae. Seedlings infested with 0, 1000 and 8000 Pratylenchus coffeae nematodes were exposed to 14CO2 and the incorporation and distribution of radioactivity were followed in the roots, stems and leaves. Fresh mass, pigments, soluble sugars, sucrose and specific radioactivity of sucrose in the plant parts were determined. At the highest level of infestation almost all the parameters were significantly changed showing the carbon fixation in the leaves and partitioning to the roots were decreased. Since lesion nematodes are not sedentary and do not form feeding sites that could be characterised as metabolic sinks, it is suggested that their damage is more readily expressed by the leaves, through a reduction in photosynthesis and phloem transport.

Pathogenicity of two Pratylenchus coffeae populations from Brazil on coffee plants

There is limited information on the influence of Pratylenchus coffeae on the growth and development of coffee plants, in spite of the widespread occurrence of this nematode in coffee plantations. In addition, populations of P. coffeae vary in morphological and molecular features, as well as reproductive fitness and pathological potential. The objective of the present study was to compare the pathogenicity of two Brazilian P. coffeae populations, K5 from Coffea arabica roots and M2 from Aglaonema sp. roots, in terms of their influence on the plant growth and photosynthesis of Arabian coffee (C. arabica). Five experiments were conducted in controlled conditions, and the results demonstrated that K5 is pathogenic on coffee, as it can reproduce and causes obvious damage on the plant. Moreover K5 proved to be very virulent on Arabian coffee, considering its effects on seedling mortality, plant growth and photosynthesis. By contrast, M2 was considered to be of low virulence, or even non-pathogenic, on coffee because it failed to reproduce. Thus, the results indicate that K5 and M2 may be distinct species, supporting the hypothesis of previous authors.

Patogenicidade de Pratylenchus coffeae em plântulas de cafeeiro cv. Mundo Novo

The pathogenicity of two isolates of Pratylenchus coffeae from Brazil on coffee (Coffea arabica) seedlings cv. Mundo Novo was evaluated in two greenhouse experiments. In the first, the effect of initial population densities (Pi = 0; 333; 1,000; 3,000 and 9,000 nematodes per plant) was studied using an isolate of P. coffeae from Marilia, SP, Brazil (host: coffee). The data were adjusted for the Seinhorst non linear model Y = m + (1-m).Z Pi-T. At the end of the experiment (270 days after inoculation), all plants infested with 9000 nematodes and most of those infested with 3000 were dead. Growth and photosynthesis were reduced, starting at 333 and 1000 nematodes, respectively. In the second experiment, two isolates of P. coffeae from Marilia and Rio de Janeiro (host: Aglaonema sp.) were compared with respect to their pathogenicity, inoculating Pi = 8,000 nematodes per plant in coffee seedlings with two pairs of true leaves. Although photosynthesis was similarly reduced by both isolates, the Marilia isolate caused intense darkening of the roots, leaf chlorosis and stronger reduction of root and shoot growth. In both experiments, multiplication factors of the isolates were low, indicating that coffee is a poor host for both isolates of P. coffeae. The differential pathogenicity observed in the second experiment supports previous results in the literature showing differences between these isolates concerning morphological features and host ranges.