Oil palm rachis length was determined on primordia dissected from palms planted at four densities. It started to increase rapidly in leaf–10, that is, about ten leaves younger than the spear leaf in all density treatments. The mean number of leaf primordia at the three higher palm densities was 47.7 compared with 51.5 at the lowest density of 56 palms ha-1. Some of the palms planted at the highest density were thinned to identify the stage at which the amount of light affected the rate of leaf opening. A sudden increment of light accelerated leaf production at both the rapid expansion stage and the preceding slow expansion stage. The greatest acceleration of leaf production began 24 months after thinning, probably because of the effect of the extra light on the rate of leaf initiation. The response of leaf production to thinning may apply to other related cultural practices.

Desarrollo de hojas en la palma aceitera (Elaeis guineensis) y determination de la tasa de apertura de las hojas

The effect of simulated drought on the germination of Striga hermonthica and Alectra vogelii was studied in growth cabinets. Drought stress was applied either during the preconditioning of the seeds or at the time of application of the germination stimulant. The response of these weeds to a range of alternating day/night temperatures during germination and their attachment to the host plant was also investigated using root chambers. During the preconditioning period S. hermonthica was not sensitive to variation in osmotic potential between 0 and −1.5 MPa but A. vogelii required longer preconditioning periods at −1.2 and −1.5 MPa. The germination of both parasites was significantly reduced by increasing the osmotic potential of the stimulant. Optimum day/night temperatures for germination and attachment of S. hermonthica were 30/20° and 35/25°C, and of A. vogelii 25/15° and 30/20°C. Deviation in temperature from the optimum significantly reduced the germination and attachment of both parasites. The results show that S. hermonthica is more adaptive to adverse climatic conditions of increased osmotic potential and extreme temperatures than A. vogelii.

Efecto de la sequia y la temperatura en malezas parasiticas

Two contrasting clones of cassava (Manihot esculenta) were reciprocally grafted to test the hypothesis that the yield of cassava is limited by the number of storage roots. Effects of the root sink on leaf gas exchange were also tested under field conditions using a portable infra-red gas analyzer. Storage root number and root yield were affected by stock size and root yield was associated with the number of storage roots. The harvest index and sink-source ratio (root numberz/leaf area index) were correlated with root number. A feedback effect of root number on single-leaf photosynthesis was observed in one clone. It is concluded that the number of storage roots may be used as an indicator of sink strength.

Irrigation responses of three locally adapted onion cultivars were studied in drainage type lysimeters and under field conditions on a deep sandy loam soil, free of salinity problems, at Maradi in Niger. Evapotranspiration (Et) was established by the water balance method, and used to establish the rate of water use. The peak rate of water use was 7.5 mm per day during the bulb formation stage. Irrigating onions when the available soil moisture to a depth of 20 cm had been depleted by 40% increased the yield more than irrigation at 60 or 80% depletion. The mean yield from plots receiving frequent irrigation was 33 t ha−1.

Evapotranspiratión de la cebolla en el sahel nigeriano

The possibility of growing dry peas in the semi-arid areas of Mediterranean countries was assessed by comparing dry pea (Pisum sativum L.) varieties with the highest yielding barley and durum wheat varieties under rainfed conditions and with supplementary irrigation in Cyprus. The yield of barley cv. Kantara was greater than that of the best pea variety selected, PS 210713, especially under the driest conditions, but the differences between cereals and dry pea varieties were smaller when grown in areas where there was more rain or where supplementary irrigation was supplied. The protein content of the dry seeds and straw of the peas was higher than those of the cereals. It is concluded that selected varieties of dry peas could be grown in dry Mediterranean areas, particularly in rotation with barley or wheat.

Pisum sativum L. para zonas mediterráneas