TEMPORAL AND SPATIAL DYNAMICS OF MICROSCLEROTIA OF MACROPHOMINA-PHASEOLINA IN 3 FIELDS IN NORTH-CAROLINA OVER 4 TO 5 YEARS

The spatial and temporal dynamics of microsclerotia of Macrophomina ph aseolina were investigated in three fields planted to common agronomic crops in North Carolina over 4 to 5 yr. Two fields, C-1 and C-2, were divided into 180 contiguous quadrats (6.1 X 6.1 m) arranged in an 18 X 10 grid, and one field, W, was divided into 144 contiguous quadrats (4.6 X 4.6 m) arranged in a 12 X 12 grid. During the period of study, inoculum density ranged from 35.3 to 77.5, 20.4 to 59.7, and 6.4 to 18 .0 microsclerotia per 10 g of air-dry soil in C-1, C-2, and W, respect ively. In C-1 and C-2, no characteristic seasonal fluctuation or gener al trend in number of propagules was found. In W, an increase in inocu lum density in the first half of each year was generally followed by a decrease in the second half of the year. A small but significant decr ease in inoculum density was found over the 4 yr of sampling in W. In each field, the propagules remained aggregated over the years of sampl ing as indicated by values of Lloyd's index of patchiness. The degree of aggregation fluctuated, which indicated the existence of factors wi th opposing effects on the level of aggregation. The level of aggregat ion usually decreased when the soil was tilled but was also probably a ffected by nonrandom deaths of propagules. Mean location (e.g., the ce ntroid of occurrence) of the propagules remained nearly constant in ea ch field over the period of study. Spatial correlation analysis and de nsity maps demonstrated the development of new foci near old ones in C -1. In C-2, no new foci formed. In W, the spatial pattern of the micro sclerotia was characterized by a relative high density on one side of the field and a relative low density on the other side during the year s of sampling. A sensitivity of spatial correlation analysis to extrem e values was observed. The observed spatial pattern of microsclerotia of M. phaseolina could not be explained by spatial variation in physic al and chemical properties of soil.