Tiller mortality and its relationship to grain yield in spring wheat
A primary determinant of grain yield in barley (Hordeum vulgare L. emm. Lam) is the number of ear-bearing tillers per plant at harvest, which depends both on the production of tillers and on their subsequent survival to form ears. This three-year field study compares tiller production and survival in relation to final grain yield in three types of barley: 2-rowed winter (2rw), 6-rowed winter (6rw) and 2-rowed spring (2rs), grown in two contrasting environments. These three types differed significantly in shoot and ear number, the winter barleys showing higher tiller production, with the maximum number of tillers ranging from 798 to 2315 m−2 in 2rw, 711 to 1527 in 6rw and 605 to 1190 in 2rs. Grain yield across environments and years was strongly correlated () with the number of ears at harvest. The maximum number of shoots produced by each type of barley was inversely related to the mean temperature during the tillering phase. Tiller mortality was inversely related to the maximum shoot production, being significantly lower in barleys with less tillering capacity, i.e. the spring type (with average values of 34.3% and 42.7% in the two environments). The highest tiller mortality occurred before anthesis and, to a lesser extent, from anthesis to maturity. These data support the hypothesis that the principal cause for tiller mortality in barley grown under Mediterranean conditions is the competition between tillers for a limited supply of resources.
Spikeless tillers of wheat (Triticum aestivum L.) affect grain yield because of less than optimum effective plant population. This study was conducted to examine the genetic variability for tiller mortality, and its relationship to grain yield in diverse wheat lines. Twenty lines were evaluated in replicated field tests in 4 years at Rampur, Nepal. The characters investigated were maximum number of tiller produced, the number of reproductive tillers, tiller mortality, and grain yield. The lines differed significantly for all characters. The tiller mortality ranged from 7 to 30%. There were substantial effects of environment on all four characters. The entry-by-year interactions were significant for all traits, primarily because of changes in the relative genotypic differences for these traits in the four years. However, certain lines consistently ranked low or high for tiller mortality. There was a significant negative correlation between front tine tiller and grain yield in 3 out of 4 years. There was a positive correlation of highest tiller number with reproductive tiller number and with tiller mortality. Grain yield showed a nonsignificant positive correlation with maximum tiller number. The reproductive tiller number was positively correlated with grain yield. Results of this study indicate that spikeless tillers contribute negatively to grain yield and that genetic variation exists for tiller mortality in spring wheat.
Timing of tiller initiation can also influence tiller mortality. Charles-Edwards (1984) concluded that self-thinning within plant communities is largely due to the lack of assimilate needed to continue growth and development within the individual stem which, in turn, can lead to a decrease in plant weight and eventually a decrease in plant yield. Some works have explored the purpose of rear tine tiller and the effects it may have on the plant as a whole and concluded tillers that abort may have benefited the plant due to assimilate and nutrient accumulation (Lupton and Pinthus, 1969; Palfi and Dezsi, 1960). However, Langer and Dougherty (1976) concluded that dead tillers had a negative effect on grain yield due to competition for assimilates and nutrients (Sharma, 1995).
In the destructive sample plots some samples were lost in 2011–2012. Therefore, only samples taken in 2009–2010 and 2010–2011 at TRS and BC were used in the analysis. The Proc Mixed procedure in SAS (SAS Institute, Inc.) was used to determine if there were differences in spikes m–2, kernels spike–1, weight per 100 kernels, and grain yield among site-years, mini power tiller tractor initiation period, seeding rate and N application timing. As with previous analysis, site-year, seeding rate, and N timing were treated as fixed effects; while blocks and the interactions with blocks were treated as random. When differences were detected, Fisher’s Protected LSD was used to separate means.