http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Biological control of Pythium damping-off in Amaranthus species
Several approaches to the biological control of damping-off in seedlings of Amaranthus L. seedlings by Pythium myriotylum Drechsler were investigated. One hundred twenty-six accessions of Amaranthus were screened for resistance to damping-off by P. myriotylum. Accessions ranged in resistance from very susceptible (>100.0% weighted mortality) in a vegetable cultivar of A. tricolor L. to very resistant (1.8% weighted mortality) in A. tricolor 'Early Splendor'. It was suggested that accessions that exhibited weighted percent mortalities of less than 20% be selected for use in breeding programs to breed in resistance to damping-off by P. myriotylum. Levels of oxalate and amarantin in roots and shoots of six cultivars of Amaranthus with differential resistance to damping-off by Pythium myriotylum were determined. Concentrations of neither compound were well correlated with resistance ; R^2 < 0.2 in all cases. The optimal temperature ranges for germination of seeds and growth of seedlings of Amaranthus hvbridus L. 'Quelite', for radial growth of Pythium myriotylum, and for disease development of Pythium damping-off in seedlings of A. hvbridus 'Quelite' when challenged by P. mvriotylum were determined using a temperature-gradient plate. The optimal range for germination of seeds of A. hvbridus 'Quelite' was 27.4 to 29.4 C. The optimal range for radial growth of P. myriotylum was 30.6 to 32.2 C. There was a significant correlation between disease development and temperature (R^2=0.987). The effects of three levels of light intensity on the severity of damping-off caused by Pythium myriotylum in Amaranthus hvbridus 'Quilete' were tested. The per cent mortality observed under the three light regimen (full, two-thirds, and one-third available light) were 33%, 69%, and 81%, respectively. Several biocontrol agents known to be antagonistic to Pythium species were evaluated for control of damping-off in Amaranthus cruentus L. X caudatus L. by Pythium mvriotylum. The agents were used alone and in selected combinations. Only Pythium nunn Lifshitz and a combination of Trichoderma koningii Oudem and P. nunn gave a significant reduction in seedling mortality over the positive control.