4.2 Relationship between yield and yield components
We found that grain yield in barley was reduced by waterlogging
regardless of genotype or treatment imposed (Fig. 2a, b). Yield
reductions were mainly caused by reduced spikes per m2when waterlogging occurred in early phenology. WL1-3 had similar effects
on grain yield and yield components, with reduction in spikes per
m2. This is likely to be due to the growth stage when
waterlogging treatments were imposed. WL1-3 were applied prior to/at
tillering stages (ZS12.5 and ZS15); all three treatments caused
reductions in tiller numbers (data not shown), such that spike numbers
were reduced at the end of waterlogging for all treatments except WL4.
The final number of fertile spikes at maturity depends on tiller
appearance rate (Alzueta et al., 2012) and the percentage of tiller
mortality (Baethgen, Christianson, & Lamothe, 1995; García del Moral &
García del Moral, 1995). Thus, reduced spike number in WL1-3 was mainly
a consequence of lower tillering under waterlogging similar to that seen
with nutrient deficiency (Alzueta et al., 2012) and water deficits
(Cossani, Slafer, & Savin, 2009).
Fewer kernels per spike under waterlogging was a function of reduced
spike length (Arisnabarreta & Miralles, 2006; García del Moral &
García del Moral, 1995). Westminster was the only barley genotype that
did not show a reduction in kernels per spike under waterlogging
treatments WL1-3. This may be because Westminster has relatively fewer
grain numbers per spike than other genotypes under control conditions
(Fig. 3). In contrast to spikes per m2 and kernels per
spike, waterlogging induced a
higher grain weight compared with controls in Franklin, Westminster and
Macquarie+. The increase in grain weight under waterlogging was
attributed to increased grain length in Franklin, and grain width and
thickness for Westminster and Macquarie+ (Fig. 4). Fewer kernel numbers
per spike induced by waterlogging could result in more assimilate for
grain growth and kernel weight, thus compensating for the detrimental
effects of waterlogging on other yield components to some degree.
Similar effects have been observed for wheat defoliated in vegetative
stages in which more assimilate is partitioned to kernels of grazed
crops (Harrison et al., 2011a, 2011b).