Restriction of transpiration rate under high vapour pressure deficit and non-limiting water conditions is important for terminal drought tolerance in cowpea.

Drought stress is a major constraint on cowpea productivity, since the crop is grown under warm conditions on sandy soils having low water-holding capacity. For enhanced performance of crops facing terminal drought stress, like cowpea, water-saving strategies are crucial. In this work, the growth and transpiration rate (TR) of 40 cowpea genotypes with contrasting response to terminal drought were measured under well-watered conditions across different vapour pressure deficits (VPD) to investigate whether tolerant and sensitive genotypes differ in their control of leaf water loss. A method is presented to indirectly assess TR through canopy temperature (CT) and the index of canopy conductance (Ig). Overall, plants developed larger leaf area under low than under high VPD, and there was a consistent trend of lower plant biomass in tolerant genotypes. Substantial differences were recorded among genotypes in TR response to VPD, with tolerant genotypes having significantly lower TR than sensitive ones, especially at times with the highest VPD. Genotypes differed in TR response to increasing VPD, with some tolerant genotypes exhibiting a clear VPD breakpoint at about 2.25 kPa, above which there was very little increase in TR. In contrast, sensitive genotypes presented a linear increase in TR as VPD increased, and the same pattern was found in some tolerant lines, but with a smaller slope. CT, estimated with thermal imagery, correlated well with TR and Ig and could therefore be used as proxy for TR. These results indicate that control of water loss discriminated between tolerant and sensitive genotypes and may, therefore, be a reliable indicator of terminal drought stress tolerance. The water-saving characteristics of some genotypes are hypothesised to leave more soil water for pod filling, which is crucial for terminal drought adaptation.

[Squamous cell carcinoma in black patients: 80 cases]. / Carcinome épidermoïde sur peau noire: 80 cas.

INTRODUCTION: Squamous cell carcinoma is a malignant epithelial tumor of the skin, rarely observed in "black" skin. It often complicates an acquired or congenital pre-neoplastic dermatosis. We report on 80 cases of squamous cell carcinoma having occurred in black African patients from Senegal. PATIENTS AND METHODS: We retrospectively analyzed all the medical files of patients followed-up in the department for histologically confirmed squamous cell carcinoma from 1980 to 1999. RESULTS: Eighty cases of carcinoma were collected. The mean age of the patients was of 47 years (range: 1 to 85) and the sex ratio was of 1.35 (46 men and 34 women). A pre-neoplastic dermatosis was identified in 65% the patients. Acquired pre-neoplastic dermatosis was: heat burn scars (15 cases), chronic discoid lupus erythematosus (6 cases) and chronic phagedenic ulcer (4 cases). Pre-neoplastic genodermatoses were: albinism (6 cases), xeroderma pigmentosum (5 cases) and epidermodysplasia verruciformis (1 case). Lesions were multiple and cephalic in patients with genodermatosis. Death due to carcinoma occurred in 8 patients. COMMENTS: This large series of squamous cell carcinoma emphasizes: the rarity of squamous cell carcinomas in black patients and the frequency of its occurrence on acquired pre-existing dermatosis. For many years phagedenic ulcers predominated. Our results show the regression of the latter and its increase on post-burn scars and chronic lupus erythematosus. Pre-neoplastic genodermatoses that determine multiple cancers, usually located on sun-exposed areas and occurring in young patients, are particularly severe.