Defoliation and defoliants

Effects of pre-harvest chemical application on rice desiccation and seed quality

Pre-harvest desiccation may increase the efficiency of seed production. Field studies were conducted to determine the effects of diquat, paraquat, and ethephon applications on grain moisture, grain weight, and seed germination of hybrid rice Yanliangyou 88 (Oryza sativa ssp. indica) and conventional rice Wuyunjing 7 (Oryza sativa ssp. japonica). In 2013, we tested 12 treatments applied at four weeks (Yanliangyou 88) and six weeks (Wuyunjing 7) after heading. Results showed that reductions in moisture content were significant two and four days after chemical application. Chemical applications had no adverse effects on 1000-grain weight, germination percentage, or germination index, but there were negative effects on the percentage of normal seedlings. Desiccation effects increased with increase in the period after application, while the effect of ethephon combined with diquat or paraquat on desiccation was limited compared with that of diquat or paraquat alone in a short period after application. In 2013, chemical applications reduced the moisture content by from 0.5% to 6.4%, the germination percentage by from 0% to 3.3%, and the percentage of normal seedlings by from 13.3% to 100.0%. Among the treatments, diquat applied at 120 g/ha resulted in effective desiccation with fewer negative effects on grain weight and seed germination in 2013 and 2014. Therefore, diquat may have potential as a pre-harvest chemical desiccation treatment for rice. These results may provide a basis for developing and implementing protocols for large scale field trials.

The influence of non-cytotoxic concentrations of the herbicide 2,4-dichlorophenoxyacetic acid on the DNA synthesis in cultured vertebrate cells

The influence of the herbicide 2,4-Dichlorophenoxyacetic acid on the growth of cultured chicken muscle cells was studied by observing morphological changes and by cytophotometric measurement of the DNA content of individual cells. DNA-synthesis curves were derived from the distribution of DNA values. No marked effects were observed at a concentration of 60 mug per liter. In contrast, doses of 600 mug per liter caused a loss in cell differentiation consisting of a partial lack of polar orientation, diminished formation of fibers, and an increase of the N/C ratio. The nuclear matrix of desoxyribonucleoprotein (DNP) changed to a more heteropycnotic structure. Isolated cell necroses were found after 44 hrs of exposure. When compared to the controls, the relative DNA synthesis time was found to be prolonged 1.5-fold. The number of cells in the G2 phase decreased during 44 hrs of exposure. It is concluded from these results that the dosedependent growth inhibition of 2,4-D on vertebrate cells in culture takes effect during DNA synthesis. The morphological changes of the nuclear structure suggests that 2,4-D directly affects the template activity of the DNP matrix.

Ethylene: a factor in defoliation induced by auxins

Aerial sprays of synthetic auxins defoliate many species of tropical trees. Treatment of Euonymus japonica leaves with the n-butyl ester of 2,4-dichlorophenoxyacetic acid causes premature senescence and leaf fall and stimulates ethylene production by the blade 5-to 25-fold. Exposure to ethylene alone similarly accelerates senescence and leaf fall. Evidence indicates that the defoliant action of auxin is mediated through the enhanced amounts of ethylene in the blade.