Abstract
Many in situ conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization, but little is known about the effectiveness of the developed programs in conserving plant genetic diversity. We investigated the effectiveness of an unregulated (i.e., unplanned or open) conservation system maintained by Thai farmers in conserving Thai elite cassava (Manihot esculenta Crantz) varieties. Specifically, we compared genetic diversity of 266 cassava clones that were collected from 80 farms in eight provinces with 16 cassava landraces and varieties released since the 1970s through genotyping with 35 informative simple sequence repeat (SSR) markers. The SSR analysis revealed a large regional heterogeneity in cassava diversity, with a strong genetic differentiation of the assayed clones among the 80 farms (19.8 %) and across the eight provinces (11.8 %). Significant associations were also found between SSR variation and farm agro-ecological factors or some farming practices. However, there was no significant genetic differentiation (0.9 %) between the 266 farm clones and 16 reference varieties. These findings suggest that the Thai elite cassava genetic diversity was fortuitously conserved by the farmers through farming with different sets of varieties. Implications of these findings are discussed with respect to on-farm conservation of plant genetic resources.
Highlights
Recent decades have seen an increasing role of in situ conservation of plant genetic resources (Maxted et al 1997; Jarvis et al 2007; Padulosi et al 2012), and many in situ and on-farm conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization
We compared genetic diversity of 266 cassava clones that were collected from 80 farms in eight provinces with 16 cassava landraces and varieties released since the 1970s through genotyping with 35 informative simple sequence repeat (SSR) markers
There was no significant genetic differentiation (0.9 %) between the 266 farm clones and 16 reference varieties. These findings suggest that the Thai elite cassava genetic diversity was fortuitously conserved by the farmers through farming with
Summary
Recent decades have seen an increasing role of in situ conservation (i.e., the conservation in its natural habitat) of plant genetic resources (Maxted et al 1997; Jarvis et al 2007; Padulosi et al 2012), and many in situ and on-farm conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization (e.g., see Vetelainen et al 2009). No specific efforts have been documented to develop an official on-farm conservation program for local, adapted cassava germplasm (FAO 2010) This may reflect the fact that cassava varieties are largely clonally propagated; there are few unique landrace varieties in Thailand (Hershey and Debouck 2010); and most importantly, the official varieties released since the 1970s are conserved in the Thai cassava collection. Thai agricultural farming has been modernized since 1960s and may differ from those traditional cassava farming systems in South America in variety acquisition, plantation, and maintenance (Ratanawaraha et al 2001), as the transition has been made for Thai cassava from a staple food to products and raw materials for the processing industry (FAO/IFAD 2001) and the adoption rate of new varieties by farmers is high (Debouck et al 2011). The specific objectives of this investigation were to (1) compare the genetic diversity and structure of 266 cassava clones of unknown genetic background that were collected from 80 farms in eight provinces with 16 Thai cassava landraces and varieties released since the 1970s through genotyping with 35 informative SSR markers, (2) identify
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