Author : Phan Ei Phyu

Summary : Agronomists and plant breeders usually rely on the evaluation of various plant
traits in the field to select cultivar for further breeding step. Agronomic, physiological
traits and yield component traits, and their relationship with grain yield were determined
in various germplasm sets in IRRI irrigated breeding program. Physiological and yield
component traits were investigated in the Diversity Panel with 36 genotypes in 2015 WS
and 2016 DS, 36 genotypes including parent and offspring lines developed by Rapid
Generation Advance method (RGA) in 2016 DS, advanced breeding lines of Multi-
Environmental Yield Trial (MET) stage at 2015 WS, and advanced breeding lines of
Regional- Yield Trial (RYT) and Preliminary-Yield Trial (PYT) under alternate wetting
and drying (AWD) and normal irrigation conditions at 2013 DS and 2014 DS. Spectral
reflectance measurements for normalized difference vegetation index (NDVI) at key
growth stages were done to estimate physiological status of plant genotypes, and evaluate
the usefulness of this tool in phenotyping. The NDVI at different growth stage, SPAD at
4 WAH, agronomic traits, yield component traits and yield were collected to measure the
heritability, relationship of traits with yield in various germplasm sets.

There was a differential response of different germplasms in terms of yield
component traits. In Diversity Panel, plant height, the number of panicle per m2, number of spikelets per panicle, HI, 1000 GW, NDVI at heading stage, NDVI at late-grain filling
stage and SPAD at 4WAH were highly associated with yield, and thus these traits can be
used as reliable selection index for yield improvement during wet season (WS). During
dry season (DS), plant height, NDVI at panicle initiation and NDVI at late-grain filling
stage were more highly associated with yield. For Diversity Panel, the degree of genetic
variation among the genotypes and the different seasons were observed.

Plant height, panicle length, NDVI at panicle initiation and NDVI at late-grain
filling were highly associated with yield in parent and advanced breeding lines of RGA
method during DS. Thus, the improvement of these traits is possible through
hybridization followed by selection to release high-yielding variety for DS. The different
trait selection for early- and late-maturing lines in MET trail stage could be more
effective to identify high-yielding advanced breeding lines. A very strongly association of
yield with biomass under water-saving (AWD) condition, and number of spikelets per
panicle and HI are good selection traits under both AWD and normal irrigation condition.