Adaptation of rice (<i>Oryza sativa</i> L.) genotypes in the rainfed uplands of southern Laos

Summary In southeast Asia, upland rice ( Oryza sativa L.) is typically grown by subsistence farmers under shifting cultivation systems in mountainous regions. In Laos, glutinous upland rice is grown in the north and along the Laos-Vietnamese border in central and southern regions. Previous research has examined requirements for upland rice in northern Laos, but not in the south, which is lower in altitude, with higher evaporation. This paper examined the adaptation of six upland rice genotypes, (preferred traditional tropical japonicas Nok and Mak Hin Sung, preferred traditional indicas Laboun and Non, and improved indica B6144F-MR-6-0-0 (B6144), which were compared with a tropical japonica Local Check (which varied from site to site), over seven sites (from new to continuous cultivation) in southern Laos. Mean grain yield of the site ranged from 1.04 to 3.71 t ha −1 , with higher yields in the wetter year 2011 than in the drier 2012 (3.19 t ha −1 with 1718 mm vs 1.23 t ha −1 with 1034 mm rainfall). Nevertheless, cluster analysis identified three sites and three genotype groups, which were not simply related to annual rainfall. Three principal component axes were associated with yield potential (PCA1), cultural history (PCA2), and resource limitation as the growing season progressed (PCA3). Consequently, upland rice response was related to 4 cultural history by year groups: Nong 2011 (E1: new cultivation, wet year, high yield potential), Xepon 2012 (E2: old cultivation, dry year, low yield potential), and intermittent stress (E3) associated with either old cultivation in a wet year (Xepon 2011) or new cultivation in a dry year (Nong 2012). Among genotypes, Nok, Non, and Laboun were high-yielding over sites (2.30 t ha −1 ), B6144 and Local Check were low yielding over sites (1.69 t ha −1 ), while Mak Hin Sung was highest yielding in the Xepon 2012 sites only (1.62 t ha −1 ). The results suggested a stronger importance of water deficit in southern Laos, especially during grain filling. Nevertheless, genotypes which performed well in southern Laos, the early indica Laboun and the specifically adapted tropical japonica Mak Hin Sung, were adopted by upland farmers in the south, and were still being grown there seven years later. Relative to upland and aerobic rice for northern Laos, which is exposed to only mild or intermittent water deficit, upland rice for southern Laos requires greater tolerance to water deficit.