Individuals infected with Leishmania major usually acquire immunity to cutaneous leishmaniasis. In this study we have investigated peripheral blood mononuclear cells (PBMC) stimulated by Leishmania antigens in two groups of Sudanese individuals, one with a history of cutaneous leishmaniasis and one living in an area without the disease. The production of interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 was investigated in culture supernatants, and the cellular sources of IFN-gamma and TNF-alpha were identified. Cells from individuals with a history of cutaneous leishmaniasis produced significantly higher levels of IFN-gamma and TNF-alpha than cells from individuals without a history of the disease. Similar levels of IL-10 were found in the two groups. Flow cytometric analysis revealed high numbers of CD3+ cells producing IFN-gamma and TNF-alpha, and only a few CD3+ cells containing IL-10, in the PBMC cultures from the individuals with a history of cutaneous leishmaniasis. Interferon-gamma and TNF-alpha were predominantly produced by CD4+ T cells rather than CD8+ T cells. The results suggest that cellular immunity against cutaneous leishmaniasis is mediated predominantly through antigen-specific CD4+ T cells in individuals with a history of cutaneous leishmaniasis.

Wheat plants in an irrigated field crop were fertilized with 0 (N0), 3 (N3), 10 (N10) or 30 (N30) kg nitrogen ha-1 week-1 for 10 weeks, commencing 12 days after sowing, till the flag leaf reached maturity. Nitrogen significantly increased tiller numbers, dry matter and grain yields per plant. Maximum plant size resulted from the N30 treatment, but maximum grain yields per plant from the N10 treatment. Total spikelet numbers increased with increasing nitrogen supply up to the N30 treatment, and this was due to increased rates of spikelet primordia production. Nitrogen treatments had almost no effect on the duration of spikelet primordium formation. Only two ear-bearing tillers were produced in the N10 and N30 treatments, and none in the others. Tiller apices had a similar, or in the case of the second tiller of N30 plants a 29% higher, rate of spikelet primordia formation to that of the associated main shoot, and all apices formed terminal spikelets at a similar time. The second tiller did not initiate primordia production until 25% of final spikelet numbers were present on the main shoot apex. The higher grain yield per plant in the N10 than in the N30 treatment was due largely to more grains per fertile spikelet on the tillers of N10 plants. It was speculated that the poorer performance of tillers on N30 plants was due to mutual shading of shoots and/or poorer nitrogen nutrition of the tiller apices owing to the method of nitrogen application. It was concluded that nitrogen supply affected grain yield per ear more by influencing the ability of florets to set grain than by varying spikelet number.

Continuous removal of tillers from wheat plants (cv. Gamenya) in an irrigated field crop resulted in an 86% increase in grain yield of the ear on the main shoot due, principally, to more kernels per fertile spikelet. On detillered plants 99% of spikelets were fertile with an average of 3.8 kernels per fertile spikelet compared with 91% and 2.4 for the control. Tiller removal increased spikelet numbers by 1 to a mean of 21.4 but did not affect the rate of production of spikelet primordia. The concentration of sugars (glucose, fructose, sucrose) in leaf bases at terminal spikelet formation and in leaf bases and ears just before ear emergence were the same in control and detillered plants. It was considered unlikely that tillers compete with the main shoot for carbohydrates thus limiting ear development and grain yields of the main shoot; instead, competition for reduced nitrogen may be involved. Shading plants to 20% of full sunlight, especially during floret development, reduced grain yields per ear by 50% due to fewer kernels per fertile spikelet (2.2) plus a 32% decline in kernel weight. Tiller numbers and shoot size were reduced by shading while spikelet numbers were reduced by two compared with controls due to a reduced rate of production of spikelet primordia. Shading also reduced sugar concentrations relative to controls in leaf bases at terminal spikelet formation and in ears just prior to emergence. The supply of carbohydrates under shading was limited, affecting growth and grain yields.