Can wild relatives of sorghum provide new sources of resistance or tolerance against Striga species?

Summary The genus Striga contains some of the most noxious parasitic plants, which have a devastating impact on cereal production in Africa; of most importance are Striga hermonthica and Striga asiatica . Complete resistance to infection by Striga species does not exist in cultivated cereals. Of great interest is the possibility that wild relatives of cereals may provide a genetic basis for resistance or tolerance to infection and may be of enormous value for the development of resistant crops. A wild relative of cultivated sorghum, Sorghum arundinaceum , demonstrated tolerance to infection by S. asiatica , with little impact of S. asiatica on host growth or grain production compared with the detrimental impact of the parasite on cultivated sorghum. Infection by S.hermonthica , however, had a significant influence on host performance for both wild and cultivated sorghum. Differences in host:parasite responses may be explained by the timing of parasite attachment and differences in host specificity for these two Striga species.     

水分胁迫对番茄叶片气孔传导及光合色素的影响

以栽培番茄品种AilsaCraig的6叶期幼苗为试验材料,在水培条件下研究了50,75和100g/LPEG水分胁迫对叶片气孔传导、光合色素含量及发叶速度的影响。结果表明,水分胁迫使气孔传导度和发叶速度降低,光合色素增加。气孔传导度和发叶速度的降低均与水分胁迫强度和持续时间有关,而光合色素的增加主要与胁迫持续时间有关。     

Nutrient cycling in a Pinus patula plantation in the Mpumalanga Province, South Africa

The accumulation of litter on the forest floor was identified as a potential problem in managed plantations of Pinus patula (Schlechtd. et Cham.) in the Mpumalanga Province of South Africa in the late 1980s. Litter accumulation in pine plantations is regarded as a threat to site productivity as organic acids are released, moisture penetration is altered and nutrients are immobilised within the litter. This study examines the cycling of nutrients in a 42-year-old P. patula stand in which litter has accumulated. Samples of the vegetation, litter and soil components were collected and chemically analysed for total nitrogen (N), phosphorus (P) and the major cations potassium (K⁺), calcium (Ca²⁺) and magnesium (Mg²⁺). Complete nutrient budgets for N and P, and the cation pool sizes were determined. It was evident from these studies that large reserves of N (1442 kg ha⁻¹) and P (103 kg ha⁻¹) are stored in the litter layers, with levels of cations being low. The presence of large nutrient reserves within the litter and the predominance of fine feeder roots distributed within this layer indicated that a tightly closed plant–litter–plant nutrient cycle was in operation for the cycling of N and P. This may not be true for the major cations. Management of the litter should ensure retention of as many nutrients as possible in the system. This could be achieved through controlled burning to reduce nutrient loss through volatilisation; increasing forest floor temperatures by altering the planting density and application of dolomitic lime to replace cations and to alleviate the acidic conditions making the litter more favourable for decomposing organisms.     

Characteristics, prevalence and aetiology of lesions of the oral mucosa in adult sheep

A total of 214 sheep with lesions of the oral mucosa were recorded at the Veterinary Laboratories Agency regional laboratories between March 15, 2002 and February 28, 2003. Using denominator data from the scrapie abattoir survey a prevalence of 0.95 per cent (95 per cent CI 0.82 to 1.10 per cent) was recorded, and using the fallen stock survey a prevalence of 1.15 per cent (95 per cent CI 0.64 to 1.91 per cent) was recorded. The lesions varied widely and included dental pad lesions in 20 per cent of cases. In total, 248 sites were affected, the commonest being the lower gum below the incisors, which was affected in 100 sheep. Most of the lesions were 1 cm or less in diameter. Ninety per cent of the 251 lesions examined histologically were erosions, ulcers, healed ulcers, focal epithelial necrosis or haemorrhages, and the changes observed indicated that trauma was the most likely primary cause.