Field drying is a traditional practice carried out by farmers in Uganda and it is one of those practices reported to affect the postharvest quality of maize. A study was therefore conducted to establish the effects of delayed harvest on moisture content, insect damage, moulds and aflatoxin contamination of maize in Mayuge district. Sixteen farmers were selected from Bayitambogwe sub-county, eight from each of the villages of Bugodi and Musita. Maize was sampled from each farmer's field in 2003B and 2004A seasons at harvest stages of physiological maturity and after delayed harvest for 1, 2, 3 and 4 weeks. Each sample was analysed for mould incidence, moisture content, insect damage and aflatoxin contamination. In each season, mould incidence, insect damage and aflatoxin levels significantly (P < 0.05) increased with delayed time of harvest. Moisture content reduced with delayed harvest time but the maize did not dry to the required safe storage moisture content of ≤15%. Seasonal effects were only significant for moisture content: the 2003B crop had consistently lower moisture content than 2004A crop. These results indicate that, for improved harvest quality of maize, farmers should harvest no later than 3 weeks after maize has attained physiological maturity.

Three maize (Zea mays L.) hybrids were evaluated for their grain yield under different levels of spring‐applied anhydrous ammonia fertilizer. The N content in the vegetative tissues and grain was analyzed at the midsilk stage and at 60 days after pollination. Of the three hybrids tested, B14 ✕ Oh43 (intermediate type) responded to moderate levels of N fertility, B73 ✕ Mol7 (high‐fertility type) had a great response to additional N, and Pioneer 3732 (low‐fertility type) performed well under low levels of N fertilizer but reached maximum yield with only 67 kg N/ha. There are at least three factors affecting grain yield which distinguish the high‐fertility from low‐fertility type hybrids. These include 1) ability to absorb additional N fertilizer after the midsilk stage, 2) rate and duration of grain fill, and 3) rate of zein synthesis (kernel N sink) affected by N fertilizer. When the kernel genotpye of Pioneer 3732 was modified by pollinating with pollen from B73 ✕ Mol7, the developing F1 kernels not only had grain protein concentration higher than Pioneer 3732 F2 kernels but had dry matter accumulation kinetics complementary to Pioneer 3732 and B73 ✕ Mol7. This complementation resulted in larger kernels than those obtained with selfed kernels of either hybrid. This result indicates the kernel sink is more important than the vegetative source in affecting kernel weight and grain yield.

Eight maize (Zea mays L) hybrids were grown under five N levels with or without the nitrification inhibitor, nitrapyrin (2-chloro-[6-trichloro-methyl] pyridine), to evaluate N interactions relative to yield performance, N use efficiency, grain protein concentration, and kernel texture. Results indicate that maize hybrids can be grouped into three categories based on grain yield: (1) low N-responsive types which reach their maximum yield with 134 kg ha-' of applied N ; (2) intermediate types that respond to moderate N levels (134 to 201 kg N ha-'); and (3) high N-responsive types that respond to higher levels of N (201 kg N ha-'). High N-responsive types, in general, increased yield with nitrapyrin treatment at all levels of N. Crop N utilisation efficiency for high Nresponsive hybrids decreased, but was static for low N-responsive hybrids as N fertiliser increased. In general, as the grain yield of a hybrid increased in response to N, the concentration of protein in the kernel increased; although grain yields and protein concentration are negatively correlated among hybrids. Increased kernel translucence, an indicator of kernel hardness induced by N fertiliser, correlated highly positive with zein proteins. Isoelectric focusing analysis showed that increases in zein were primarily due to a quantitative increase in a-and y-zein polypeptides. This study indicates that hybrids are different in their N requirements for maximum yield. Low N conditions not only restrict grain yield but also affect kernel textural quality.

This study was designed to evaluate the relationship of zein content with yield potential of maize (Zea mays L.). Maize cultlvars were grown under different rates of N (0 to 201 kg/ha) with and without nitrapyrin (0.55 kg/ha) added to correlate protein content, kernel weight, and grain yield. Carbon‐14 dioxide was applied to maize hybrid, Pioneer 3369A, to determine the effect of N on sucrose translocation into kernels. The results indicate that zein and glutelins combined may serve as a functional N sink in the kernel to affect starch accumulation, kernel weight, and yield; however, zein may be more effective because its synthesis can be manipulated readily by N fertilization and genetic means. A positive correlation between zein content, kernel weight, and grain yield was consistently observed. The quantities of zein produced vary according to the amounts of N fertilizer applied. The increase in zein with higher rates of N fertilization (up to 201 kg/ha) did not decrease the nutritional quality of seed protein because increases in germ size and a slight increase in non‐zein protein in the endosperm occurred concurrently. Based on this data, the selection of maize hybrids which are capable of producing maximum amounts of zein with additional available N should provide a means of increasing kernel weight and grain yield through the greater N sink potential of these hybrids.

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Zea mays grown with high levels of N fertilizer transports more sucrose into kernels than with low N. Sucrose translocation was greatest in genotypes with the highest capacity to deposit nitrogenous compounds as zein and glutelin in the kernel. These two proteins combined contain about 80% of the total N in the kernel and about 60% of the total N in the plant at maturity. They appear to serve as a functional N sink for the deposition of nitrogenous compounds. As the N sink capacity increases with additional available N fertilizer, more sucrose is transported into the kernel, resulting in increased kernel weight and grain yield. Zein functions as a more dynamic N sink than glutelin because the synthesis of zein is readily manipulated by N fertilization and genetic means. Increases in N deposition in the normal endosperm induced by N fertilizer are confined primarily to zein. Early termination of zein accumulation in the opaque-2 mutant results in a reduction of sucrose movement into kernels. By using plants heterozygous for normal and opaque-2 in these studies, interplant variability was eliminated and the hypothesis relating the kernel N sink capacity to productivity was strengthened.Our previous studies (21) have suggested that zein and glutelin serve as a N sink in maize (Zea mays L.) kernels to regulate the movement of photosynthates into kernels. Although both ammonium and nitrate ions can be taken up by maize roots, the assimilation of ammonia and its subsequent organic N interconversions require readily available organic acids, e.g. a-ketoglutaric acid (12), which are derived from sucrose. In response to high concentrations of ammonia, a greater amount of sucrose is translocated from leaves to provide energy and essential carbon skeletons for ammonia assimilation and organic N interconversions (25). Concurrently, the movement of sucrose to N-rich tissues may enhance CO2 fixation in leaves (13). The increase in photosynthetic efficiency, and the translocation of nitrogenous compounds and sucrose into the kernel sink for photosynthates, should further promote the synthesis of starch and thereby increase yield. Since nitrate, unlike ammonia, may accumulate without assimilation (18) be made available for assimilation (8). It seems that the effectiveness of the ammonium ion in enhancing sucrose movement is facilitated by the rapid assimilation of ammonia by roots and the resultant deposition of amides and amino acids in some tissue. These nitrogenous compounds are stored temporarily in the stalk and leaves during the period of vegetative growth. About 60% of the final N in maize kernels is present in the vegetative tissues at pollination; the remaining 40% is obtained from the soil subsequently (7). As the endosperm develops, the proteins in vegetative tissues are turned over, and the amino acids and newly assimilated N are transported into the kernel (2, 6). We propose that zein and glutelin function as N sinks for the deposition of these nitrogenous compounds to facilitate the movement of photosynthat...

A diallel cross of seven inbreds and one synthetic line of maize were analyzed in 1994 and 1995 for their reaction to Diplodia ear rot. An additional inbred line was included in the 1995 analysis. Plants were inoculated by placing a pycnidiospore suspension (5 × 103 spores per ml) of Stenocarpella maydis in the whorl at the V14 to V15 growth stage. Crosses were evaluated for disease incidence of Diplodia ear rot at harvest, and the percentage of plants with Diplodia ear rot in a plot was used for analysis. In both years, general combining ability (GCA) effects were significant. In 1995, specific combining ability effects were also significant. There were no reciprocal effects. There was no significant interaction between year and genotypes, indicating that crosses reacted the same in both years. Inbred lines B37, H111, B68, and MS had negative GCA effects that contributed toward resistance in both years. VA26, with intermediate resistance to Diplodia ear rot, contributed toward susceptibility. Only inbred lines with a high degree of resistance should be used as parents.