Annual report for the year 1958

Abstract

In the section (pp. 140-148) of this report [cf. 35, p. 591] dealing with phytopathological work at Yangambi Research Centre, Belgian Congo, it is stated that during 1955 infection of coffee crowns by Corticium salmonicolor was more frequent than in most years. Rust (Puccinia polysora) [35, p. 592; 36, p. 174] spread to most of the maize fields, but did not reduce yields. Helminthosporiosis affected all maize [Helminthosporium turcium] and rice [Ophiobolus miyabeanus [Cochliobolus miyabeanus]] plantings and was rather severe on sugar-cane [H. spp.]. Early in the year primary and secondary infections of bananas by bunchy top [virus: map 19] were observed. Numerous cases of root rot of cassava due to Armillaria mellea, Fomes lignosus, and Botryodiplodia theobromae were noted. A leaf disease of pepper [Piper nigrum] was caused by Rhizoctonia [Corticium] solani; removal of infected, fallen leaves at frequent intervals kept incidence reasonably low. The crowns of Eucalyptus spp. were attacked by C. salmonicolor and the leaves by C. solani. In the section dealing with Hevea rubber (pp. 50-67) it is stated that in a test of varietal resistance to brown bast [35, p. 591] clones BRI and Y0.756 had, respectively, 20 and 3 per cent. infection. Infection by Fomes [? lignosus] was less on heavy than light soil whether the clearing had been burnt or not [loc. cit.]. Six years after grafting 24 per cent. of the trees planted immediately after clearing were dead, compared with 13 per cent. of those planted after three years and 5 per cent. after nine years. In trees four years old or less 16 per cent. of the deaths were attributable to Armillaria [mellea: loc. cit.], the corresponding figures for trees five and six years old being, respectively, 32 and 44 per cent. On a heavy soil (30 to 35 per cent. clay) the death rate due to root rots eight years after planting seedlings was 5 per cent. among trees receiving the usual surgical treatment plus 2 per cent. copper sulfate; 17 per cent. among trees the base of which had been laid bare and then covered up again; and 24 per cent. among the untreated. On a light soil (20 to 30 per cent. clay), where trees had been grafted in situ, ten years after grafting the population was 80 per cent, of the original one for the treated trees and only 46 per cent. for the untreated. Microclimatic conditions have important effects on the spread of Helminiho-sporium heveae [34, p. 584]: nurseries in open situations were severely affected, while those in more confined or slightly shaded places had only very slight infection. When a group of infected trees was provided with slight shade the leaves that developed subsequently were protected against infection, though the leaves of unshaded trees continued to bear lesions. In the report from the experimental planting at Mukumari, Central Congo (pp. 333-337), it is stated that the rubber clone M8 showed good resistance to attack by [Oidium O. heveae]. In the report from the Phytopathological Laboratory, Kaniama Station, Haut-Lomami, (pp. 453-462), figures are given showing that two soil injections 17.5 cm. deep each of 4 ml. of a mixture of equal parts dichloropropene and dichloropropane or surface treatment with calcium cyanamide 2, 500 kg. per ha. greatly reduced differences in susceptibility to bacterial wilt (Xanthomonas [Pseudomonas] solanacearum) among five varieties of Virginia and seven of Kentucky tobacco. Among the former, Vamorr 48 and Dixie Bright were less susceptible than Yellow Mammoth and Delcrest. Of the Kentucky varieties, Virginia Dark was less susceptible than Nyasaland, Kentucky 160, Dark Fired Madole, and Single Sucker, and Dark Fired Kentucky and Western were less than Dark Fired Madole and Single Sucker. In the report from the Regional Laboratory of Phytopathology, Mulungu-Tshidinda, Kivu Sector (pp. 480-482), it is stated that in inoculation tests on material from different progenies, clone 1353 of Chrysanthemum cinerariifolium was the most resistant to Ramularia bellunensis [35, p. 592]. Of various products tested the following gave the best control, in descending order of efficacy: captan, ethyl mercury chloride, zineb, copper oxide; only captan was non-phytotoxic. A species of Fomes, probably F. lignosus, was relatively common on coffee and tea. A form of A. mellea with white, floury cordons quite distinct from the usual rhizomorphs was prevalent at Kivu [? on tea]. Rosellinia bunodes caused somewhat frequent infection of tea and Cinchona.