DIVERSITY IN THAILAND’S LOCAL RICE GENETIC SYSTEM
How much diversity remains in Thailand’s local rice germplasm? Which processes
contributed to genetic changes in the past, which of them are likely to continue to do so into
the future? With only one fifth the country’s rice land planted to traditional local varieties,
many of the old varieties have clearly disappeared from farmers’ field. However, planted
area tells only partial and incomplete story, and similarly number of traditional varieties that
are still grown. Most papers on in situ conservation refer to the names and types recognized
by farmers. Diversity, by definition, is measurable by the statistical term of “variance”. In
applied genetics, it refers to the variance of “a gene” within a population. Thus the variance
may be measured among alternative forms (polymorphism) of a gene (alleles) at individual
gene positions on a chromosome (loci), among several loci, among individual plants in a
population or among populations (Brown et al., 1990). Diversity may be estimated from
variances of morphological or physiological expressions of the gene. With the advent of
molecular genetics, we can now measure the variance of actual DNA sequences of a gene or
a specific length of DNA (a DNA marker). In addition to quantifying diversity by measuring
the variance of genes and DNA markers within and between populations, an understanding
of the structure and dynamics of the diversity and their causation is crucial to the management