Dennis E. Deyton

Increase in Nutritionally Important Sweet Corn Kernel Carotenoids following Mesotrione and Atrazine Applications

The herbicide mesotrione inhibits a critical enzyme, phytoene desaturase, in plant carotenoid biosynthesis. Mesotrione is currently labeled for selective weed control in sweet corn ( Zea mays var. rugosa). Mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine, acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin carotenoids in several sweet corn genotypes. Kernel lutein and zeaxanthin levels significantly increased 15.6% after mesotrione + atrazine early postemergence applications, as compared to the control treatment. It appears that mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes expressing moderate injury overcame the initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up-regulating the carotenoid biosynthetic pathway in corn kernels, which is associated with the nutritional quality of sweet corn. Enhanced accumulation of lutein and zeaxanthin is important because dietary carotenoids function in suppressing aging eye diseases such as macular degeneration, now affecting 1.75 million older Americans.

Sweet corn carotenoid concentrations influenced by herbicide applications

Carotenoids serve antioxidant functions in plant photosynthetic processes, as well as in actions of disease reduction in mammalian systems. Lutein and zeaxanthin are important dietary carotenoids in suppressing aging eye diseases. Age-related macular degeneration now affects more than 1.75 million individuals in the US. Sweet corn (Zea mays var. rugosa) is one of only a few vegetable sources high in zeaxanthin. Mesotrione herbicide is currently labeled for selective pre- and post-emergence weed control in sweet corn production. Mesotrione competitively inhibits phytoene desaturase, a critical enzyme in carotenoid biosynthesis, which results in bleaching of leaf tissues in susceptible species and eventual plant death. Sweet corn is tolerant to mesotrione applications; however, differing sensitivity exists among genotypes. What remains unclear is the impact of mesotrione on carotenoid concentrations in mature sweet corn kernels following post-emergent applications to young corn plants. Our research objective was to measure mature kernel carotenoid concentrations in response to post-emergence applications of mesotrione to genotypes of different sensitivities. Post-emergence treatments included mesotrione applied alone, or in mixtures with the photosystem II inhibitor atrazine applied to corn plants of either 5-10 or 15-20 cm in height. Kernels were harvested from mature plants and measured for carotenoid concentrations. Mesotrione applied alone, or in mixtures with atrazine acted to increase concentrations of kernel antheraxanthin, lutein, and zeaxanthin in several sweet corn genotypes. Mesotrione applications resulted in greater pools of kernel carotenoids once the sweet corn genotypes overcame initial herbicidal photo-oxidative stress. This is the first report of herbicides directly up regulating a key biochemical pathway linked to the nutritional quality of a vegetable crop.

Viscosity-temperature relationships of soybean oil emulsions and their implications for oil retention by apple and peach leaves

Summary The retention of spray droplets is influenced by properties of the spray solution such as viscosity, and by the morphology of the target surface. The objectives of this study were: (i) to determine the retention of emulsions of 1% (v/v) soybean oil with Latron B-1956®, K1™, or Telomer™; (ii) the retention of 1% (v/v) Ballistol™, 1% (v/v) Soy Gold 1000™ and 1% (v/v) Soy Gold 2000™ emulsions in water by ‘Golden Delicious’ apple (Malus pumila Mill.) and ‘Red Haven’ peach [(Prunus persica (L.) Batsch] leaves; and (iii) the influence of temperature on the viscosity of the emulsifiers used in soybean oil sprays. The viscosity of all emulsifiers, at all concentrations tested in soybean oil or in their pure form, ranging from 160 – 28,000 centipoise, declined with increasing temperature. Telomer had the greatest viscosity, followed by K1™, Latron B-1956®, and Ballistol™. Retention of soybean oil emulsions by apple and peach leaves was greatest for soybean oil emulsified with K1™ (80 and 74 μg cm−2, respectively), followed by Latron B-1956® (48 and 52 μg cm−2, respectively), and Ballistol™ (38 and 42 μg cm−2, respectively). Soy Gold 1000™ (24 and 28 μg cm−2, respectively) and Soy Gold 2000™ (9 and 14 μg cm−2, respectively) were retained least by apple and peach leaves. There were no significant differences in soybean oil retention between peach and apple leaves. This study demonstrated that the retention of soybean oil was related to the viscosity of the emulsifier (i.e., the higher the viscosity of the emulsifier, the greater the retention of the soybean oil). We suggest that soybean oil emulsions formulated for pest control would work most effectively with an emulsifier possessing high viscosity.