Reductions in kernel mass are observed when corn (Zea mays L.) kernels are grown in vitro or when unfavorable temperature occurs during endosperm cell division. We investigated the possibility that a decreased number of endosperm cells or a decreased number of starch granules is responsible for the reduced kernel mass in such environments. Three‐day‐old kernels of the single cross hybrid A619 ✕ W64A were placed in culture on a denned medium at 15, 30, and 35 °C, and their growth was compared with kernels from ears developed in the field or greenhouse. Kernels cultured at 30°C attained a final mass of 164 mg compared with 274 mg for field‐grown controls. At 30°C, endosperm cell division ceased approximately 10 days earlier, and the final number of cells was reduced by 34%. Final kernel mass was reduced by 49 and 78% when kernels were cultured at 15 and 35°C, respectively, compared with those grown at 30°C. At 35°C, the rate and duration of cell division in the endosperm, and the number of endosperm cells were severely reduced. In contrast, the rate of cell division decreased in kernels cultured at 15°C, but the duration was prolonged, and the number of endosperm cells formed was not affected. However, the number of starch granules initiated at 15 and 35°C was reduced by 70 and 97%, respectively. Final kernel mass was highly correlated with the number of endosperm cells (r=0.85,p≤0.01) and starch granules formed (r=0.76, p≤0.01). These data suggest that thermal regulation of the number of endosperm cells, starch granules, or both are mechanisms by which final kernel mass may be mediated. The reduction in mass of in vitro compared with field‐ or greenhouse‐grown kernels appears to be due mainly to a decline in the number of endosperm cells formed.

-Four potato cultivars (Solanum tuberosum L.) differing in their precocity and contrasted for their drought tolerance were investigated in the field and in the greenhouse (2 cultivars). They were subjected to two water treatments, well-irrigated and droughted. Our objective was to examine which shoot and leaf characters were related to the decrease in tuber yield. Drought reduced tuber yields by 11% in 53%. Drought stress highly reduced the dry mass of leaves in all cases. Tuber number was reduced only in early cultivars whereas in the later cultivars, leaf area index and leaf area duration were more affected than in the early cultivars. The cultivar which maintained its tuber growth rate better under drought during the first three weeks of tuber bulking also maintained its yield better. No clear common reaction of early versus later varieties to drought was found.potato / drought stress / cultivar / agro-physiological parameters Résumé -Effet du stress hydrique et du cultivar sur les paramètres de croissance, le rendement et ses composantes. Quatre variétés de pomme de terre (Solanum tuberosum L.) de précocité variable et réputées différentes au niveau de la tolérance à la sécheresse ont été testées, sous deux régimes hydriques (irrigué et stressé) au champ et sous serre. Notre objectif était d'étudier les relations entre l'évolution de différents paramètres de surface foliaire, et de masse (tiges et des tubercules) au cours du cycle et les diminutions de rendement en tubercules. Le stress hydrique a réduit le poids des tubercules de 11à 53 %. Le stress hydrique a fortement réduit la masse sèche foliaire dans tous les cas. Le nombre de tubercules a été réduit uniquement chez les cultivars précoces, tandis que les cultivars tardifs ont plus été affectés au niveau de l'indice foliaire et de sa durée. Les cultivars qui ont mieux maintenu le taux de croissance de leurs tubercules durant les trois premières semaines de remplissage ont également mieux maintenu leurs rendements. Aucune relation précocité -sensibilité au rendement sous stress n'a été observée. pomme de terre / stress hydrique / cultivar / paramètres agro-physiologiques

There are distinct phases of grain development in maize (Zea mays L.). Little has been reported on the relative effects of water deficits during the different phases of maize kernel development. Since endosperm cell number is important in determining sink capacity or strength, a water deficit during the lag phase may affect kernel development differently than one during the linear phase dominated by starch deposition. The objective of this research was to determine the effect of short‐ and long‐term water deficit, imposed during different phases of grain filling, on the pattern of maize kernel growth. We conducted two separate experiments. In the first, a short‐term (10 day) water deficit was imposed during endosperm cell division (the lag phase) or during the period of rapid starch deposition (the linear‐filling phase). In the second, a water deficit was initiated during the same phases, but extended until maturity. Plants were grown outdoors in Rabat, Morocco, in large pots arranged to achieve a stand density of 50 000 plants/ha. Short‐term water deficit during the lag phase resulted in a significant but transient delay in the accumulation of kernel dry mass. However, recovery from this delay was such that overall rate and duration of kernel growth were not affected. Similarly, short‐term water deficit during the linear‐filling phase had no effect on the rate or duration of kernel growth. When the long‐term water deficit treatment was initiated during the lag phase, kernel growth rate was not affected for approximately 24 days. Grain filling then terminated prematurely, resulting in a significant decrease in the duration of the grain‐filling period, and a 50% decrease in final kernel weight. When long‐term stress was imposed during the linear‐filling phase, kernel growth was not affected for 20 days, but then terminated abruptly, resulting in an 8‐day decrease in the grain‐filling period. Final kernel weight was not significantly decreased, however. Our results show that kernel growth is more sensitive to water deficits during endosperm cell division than during the period of rapid starch deposition. The higher sensitivity to water deficits during the lag phase was not a consequence of either a lack of carbohydrate availability to the grain, or an inhibition of starch synthesis, but was apparently due to an inhibition of endosperm cell division and the subsequent establishment of kernel sink capacity.

Although considerable information exists concerning the effect of drought on the water relations of maize (Zea mays L.) leaves, little has been published about the water relations of maize grain, or on how the process of grain filling is affected by a limited water supply. We had previously observed that the maize plant sustained normal rates of kernel growth for long periods in spite of severe water deficit during grain filling. The objective of this study was to investigate the nature of that response. Plants were grown outdoors in Rabat, Morocco, in large pots. Severe water deficit was imposed during either early or mid grain filling, and was maintained until maturity in each case. Grain water status (water potential, osmotic potential, and turgor pressure) was independent of whole‐plant water status, particularly leaf status. Photosynthesis decreased as judged by leaf water potential, diffusive resistance, leaf senescence, and total plant dry weight. Kernel growth was relatively unaffected by a water deficit that completely inhibited net photosynthate production. Kernel growth was maintained by a remobilization of stored assimilates from nongrain parts to the grain. The main source of assimilates was the stem as judged by dry weight loss and soluble sugar content. The maintenance of a high stalk moisture content in spite of severe leaf dehydration may have facilitated translocation from the stalk to the grain.

Wastewater effluent disposal is a challenge in Moroccan rural area. Wastewater treatment is the only suitable solution to overcome these environmental constraints. Technology such as MultiSoil-Layering (MSL) system is one of the most appropriate solution for the treatment of wastewater for small communities in rural areas. The MSL system overcomes many of the deficiencies of conventional soil treatment systems such as large land requirement clogging and low Hydraulic Loading Rate (HLR). The MSL systems are composed of Soil Mixture Blocks (SMB) arranged in a brick-like pattern and surrounded by Permeable Layers (PL). To investigate the efficiency of MSL systems in relation to HLR differences and the fluctuations in the wastewater contamination levels, three MSL pilot plants were alimented continuously by domestic wastewater, were constructed in three 36×30×65 cm plastic boxes, with different HLR of 250, 500 and 1000 l/m 2 /day. The main removal rates of Biochemical Oxygen Demand (BOD 5 ) and Chemical Oxygen Demand (COD) were higher at higher HLR. However, the kinetic rate constant of the MSL process implemented under Moroccan conditions is 130 d −1 at 25°C.