Estimating Incidence of Attachment of Pasteuria penetrans Endospores to Meloidogyne spp. with Tally Thresholds.

Pasteuria penetrans has .been identified as an important biological control agent of root-knot nematodes. In this study the use of tally thresholds was evaluated for estimating P. penetrans endospore attachment to second-stage juveniles (J2) of Meloidogyne spp. A tally threshold (T) is defined as the maximum number of individuals in a sample unit that may be treated as absent based on binomial sampling. Three different data sets that originated from centrifugal bioassay, incubation bioassay, and field experiments were investigated. The data sets each contained 70, 33, and 111 estimates of the mean number of endospores attached per J2 (m), respectively. Empirical relationships between m and proportions of J2 with </=T endospores attached (P(T)) were developed using parameters from the linear regression of ln(m) on P(T) (0 < P(T) < 1): ln(m) = a + b P(T), T was set to 0, 1, 2, 3, 4, 5, 8, and 10 endospores/J2. The results indicated that the variances of linear equations tended to decrease with increasing T values for all three data sets. T values of 0, 1, 8, and 10 endospores/J2 for centrifugal bioassay and incubation bioassay, and of 0, 1, 2, and 3 endospores/J2 for field experiments were associated with an r(2) of >= 0.8. These T values were robust for estimating m from P(T), reducing the variability as well as the time and effort spent in estimating the mean number of endospores attached per J2.