Improving crop productivity through higher plant density requires a detailed understanding of organ development in response to increased interplant competition. The objective of this paper is thus to investigate the characteristics of organ development under increased interplant competition. A field experiment was conducted to investigate organ development across 4 maize plant densities i.e. 2, 6, 12 and 20 plants m–2 (referred to PD2, PD6, PD12 and PD20 respectively). In response to increased interplant competition, lengths of both laminae and sheaths increased in lower phytomers, but decreased in upper phytomers. Sheath extension appeared to be less sensitive to increased interplant competition than lamina extension. Extension of laminae and internodes responded to increased plant density as soon as onset of mild interplant competition, but did not respond any further to severe competition. Both lamina width and internode diameter were reduced due to a smaller growth rate in response to increased plant density. Overall, this study identified that organ expansion rate can be taken as the key morphological factor to determine the degree of interplant competition.

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The pigeonpea (Cajanus cajan) is grown between the 45oN and 45oS as a summer food legume, and consumed by billions of people in the world. Recent renewed interest from Australian growers prompted the current study to evaluate high-yielding varieties and develop agronomic parameters for this crop. Performance of four selected pigeonpea genotypes were assessed under three row spacing (25, 50 and 100 cm) treatments and at one plant density (30 plants/m2) in two diverse Australian environments (Kingaroy and Gatton) in Queensland. Decreasing row spacing from 100cm to 25cm led to a linear increase in mean shoot dry matter (DM) at both sites. However, maximum grain yields of up to 2.9 t/ha were achieved at 50cm row spacing but the yields declined at 25cm spacing at both sites. Genotypic variation for radiation use efficiency (RUE) measured at Gatton site ranged from 1.40 to 1.76 g/MJ, which accounted for 76% of variation in DM. There was a significant effect of site and genotype on grain N and 100-seed mass. The study demonstrated that pigeonpea could be grown as a legume break crop in subtropical Australia, with potential export market opportunities.