Initial incidence and development of red core of strawberry

The initial incidence of the disease caused by Phytophthora fragariae in healthy stock of strawberry, cv. Merton Princess, was not affected by different systems of cultivation or by no cultivation for several months before preparing infested soil for planting. In disease development studies, healthy plants which were planted in infested soil in April and sampled at 35-day intervals showed symptoms of red core on 1 September. Disease severity (mean % number of diseased roots) increased with time and, when averaged over intervals of 70 days, the greatest increases occurred between the end of July and the beginning of October and between December and February. Whereas the former was due to infection of plants in which the total numbers of new roots were low, the latter was due to an increase in the numbers of diseased roots. Most primary roots were produced in October and early November and 75% of the final total were formed by 15 December. Healthy plants of the cvs Cambridge Favourite and Redgauntlet, dug from the field at monthly intervals and challenged with zoospores, were less susceptible in May and June than in other months. It is suggested that a fungicide applied in late September or October would protect the maximum number of new roots and achieve the optimum effect for a single application.     

Infectivity of Trypanosoma brucei Cultivated at 28 C with Tsetse Fly Salivary Glands*

SYNOPSIS. When transformed procyclic noninfective trypanosomes of several unrelated stocks of Trypanosoma brucei were cultivated in T-30 Falcon flasks at 28 C in a liquid medium containing head-salivary gland explants of Glossina morsitans morsitans some of the organisms developed into forms infective for mice. Infective trypanosomes were detected 7 to 14 days after the cultures were prepared and they persisted for varying periods of up to 88 days when the cultures were terminated. A few of the salivary glands became invaded with parasites about the time infective organisms appeared in the cultures. Using T. brucei TREU 929, it was shown that trypanosomes grown with between 27 and 50 explants were capable of producing infections consistently for prolonged periods. On the other hand, trypanosomes cultivated with 25 or fewer explants rarely infected mice. Infectivity titrations on trypanosome suspensions from cultures of stocks TREU 1275 and TREU 929 revealed that the maximum number of infective organisms was present 26 to 50 days after initiation of the cultures. Control cultures of trypanosomes grown in medium alone were generally not infective but 2 of the 6 stocks gave rise to a few sporadic infections. A few epimastigote-like and metacyclic-like trypanosomes were seen in stained preparations of infective inocula.     

Spatial and seasonal distribution of Culicoides imicola in Iberia in relation to the transmission of African horse sickness virus

Abstract. Collections of biting midges were made over 24 months from sixty sites spread across Iberia. Information on the distribution of the vector of African horse sickness virus, Culicoides imicola , from these 3119 samples showed that this species was annually present across south-western Spain as far as 3^o53'W and throughout most of Portugal, up to 41^o5'N. C.imicola was found in all areas where African horse sickness epizootics had occurred in 1987-90 and also in areas outside the epizootic zones.
Seasonal patterns of capture success of C.imicola , from seventeen frequently sampled sites where the vector was present, usually showed a late summer-early autumn peak. At the sites furthest south there was a discrete peak, mostly in September or October, before and after which the numbers captured increased or decreased steadily. At higher latitudes peak abundances occurred as early as May or as late as November, population build up was less uniform and numbers often declined rapidly after the peak was reached. Both the distribution and seasonal abundance patterns closely matched transmission patterns of African horse sickness virus, which rose during late summer and caused most cases during the autumn months.