No abstract

Increased aflatoxin contamination in corn by the fungus Aspergillus flavus is associated with frequent periods of drought and heat stress during the reproductive stages of the plants. The objective of this study was to evaluate the relationship between aflatoxin contamination and physiological responses of corn plants under drought and heat stress. The study was conducted in Stoneville, MS, USA under irrigated and non-irrigated conditions. Five commercial hybrids, P31G70, P33F87, P32B34, P31B13 and DKC63-42 and two inbred germplasm lines, PI 639055 and PI 489361, were evaluated. The plants were inoculated with Aspergillus flavus (K-54) at mid-silk stage, and aflatoxin contamination was determined on the kernels at harvest. Several physiological measurements which are indicators of stress response were determined. The results suggested that PI 639055, PI 489361 and hybrid DKC63-42 were more sensitive to drought and high temperature stress in the non-irrigated plots and P31G70 was the most tolerant among all the genotypes. Aflatoxin contamination was the highest in DKC63-42 and PI 489361 but significantly lower in P31G70. However, PI 639055, which is an aflatoxin resistant germplasm, had the lowest aflatoxin contamination, even though it was one of the most stressed genotypes. Possible reasons for these differences are discussed. These results suggested that the physiological responses were associated with the level of aflatoxin contamination in all the genotypes, except PI 639055. These and other physiological responses related to stress may help examine differences among corn genotypes in aflatoxin contamination.

Even though annual rainfall is high in the Delta region of Mississippi, only 30% occurs during the months in which the major crops are produced, making irrigation often necessary to meet crop water needs and to avoid risk of yield and profitability loss. Approximately, 65% of the farmland in this region is irrigated. The shallow Mississippi River Valley Alluvial Aquifer is the major source of water for irrigation and for aquaculture in the predominant catfish industry. This groundwater is being heavily used as row-crop irrigation has increased tremendously. Water level in this aquifer has declined significantly over the past twenty five years, with overdraft of approximately 370 million cubic meters of water per year. Moreover, the common irrigation practices in the Delta region of Mississippi do not use water efficiently, further depleting the ground water and making irrigation more expensive to producers due to increasing energy prices. Irrigation experts in the region have tested and verified various methods and tools that increase irrigation efficiency. This article presents a review of the current status of the irrigation practices in the Delta region of Mississippi, and the improved methods and tools that are available to increase irrigation efficiency and to reduce energy costs for producers in the region as well as to stop the overdraft of the declining aquifer, ensuring its sustainable use.

Lycopersicon pennellii (Cor.) D'Arcy possesses greater drought resistance and higher water use efficiency (WUE) than the domesticated tomato L. esculentum Mill. A previous report suggested three restriction fragment length polymorphism markers for whole plant WUE. This study identifies species differences in anatomical, biochemical, and physiological characteristics of leaves related to leaf gas exchange and whole plant WUE, which can later be tested with the molecular markers. Lycopersicon pennellii exhibited 29% lower stomatal frequency, more even distribution of stomata between the upper and the lower leaf surfaces, and a 54% thicker leaf with 31% greater air space volume relative to total leaf tissue volume than L. esculentum. Trichomes were fewer, but longer, and the ratio of air exposed mesophyll surface area relative to external leaf area was 41% greater for leaves of L. pennellii. However, this species contained 13% less chlorophyll and had 11% lower ribulose‐l,5‐bisphosphate carboxylase/oxygenase (rubisro) activity per unit leaf area than L. esculentum. The mean stomatal resistance (r8) was greater and substantially less variable among leaves of L. pennellii, but those leaves of L. pennellii and L. esculentum that had the same rs also operated at the same photosynthesis rate (A) and WUE. Therefore, differences in and WUE among the two tomato species could be fully explained by contrasting stomatal properties. Either the differences in individual leaf anatomical, biochemical, and physiological characteristics negated each other and did not substantially alter A and WUE, or the expression of the characters was linked to r8 in the same way in both species.