Path coefficient and cluster analyses of yield and morphological traits in Pennisetum purpureum.

In order to develop and select improved populations and germplasm of elephant grass for forage and bioenergy production, important morphological traits including dry matter yield, leaf:stem ratio, plant height, tillers/plant, leaf length, leaf width and stem width were investigated in 16 lines of elephant grass (Pennisetum purpureum), one purple elephant grass and hybrid pennisetum (pearl millet × elephant grass). Data were examined using correlation analysis, path analysis and cluster analysis. Plant height and tillers/plant were positively (P<0.05) correlated with yield, while leaf length and leaf:stem ratio were negatively (P<0.05) correlated with DM yield. The factors with greatest effect on DM yield were plant height and leaf:stem ratio. The elephant grasses and hybrid pennisetum were divided into 4 groups by cluster analysis based on DM yield, leaf:stem ratio, plant height etc. The 4 groups were: Group 1 dwarf type with numerous tillers, lowest DM yield and highest leaf:stem ratio; Group 2 semi-dwarf types with plentiful tillers, plus higher DM yields and plant heights and fewer tillers/plant than Group 1; Group 3 intermediate height types with moderate tillering, but higher DM yields than Groups 1 and 2; Group 4 tall types with limited tillering but highest DM yields and lowest leaf:stem ratios. Introduction Elephant grass (Pennisetum purpureum), also known as napier grass, is a warm-season perennial grass, which is widely planted in tropical and subtropical regions of the world (Wang et al. 2005). It is known throughout much of the wet tropics for its prolific growth and usage as forage for ruminants (Rusland et al. 1993; Yasin et al. 2003a, 2003b). Introduced to Guangdong and Sichuan provinces, China from Burma and India in the 1940s, it has been planted in many provinces, including Guangdong, Guangxi, Hunan, Hubei, Sichuan, Guizhou, Yunnan, Fujian, Jiangxi and Taiwan provinces in south China (Lai et al. 1998; Zhong et al. 2002; Bai and Yang 2002; Zhou et al. 2007), and is one of the most promising summer forages in the region. Owing to their tall growth habit and thick stems, tall elephant grass types have undesirable leaf:stem ratios and unacceptable nutritive value (low crude protein and digestibility) for stock, particularly as they mature (Williams and Hanna 1995), which limits their widespread use. In order to improve the quality of elephant grass as livestock feed, a hybrid pennisetum (pearl millet × elephant grass) was bred in the 1940s, which possessed both the high production potential of elephant grass and the good nutritive value of pearl millet (Pennisetum glaucum) (Osgood et al. 1997). This hybrid was introduced to Jiangsu Academy of Agricultural Sciences in the 1980s. Inter-specific crosses between male-sterile pearl millet and elephant grass were achieved after solving the key problem of making elephant grass flower at high latitudes. This was achieved by simulating a short-day environment using a black plastic cloth at the Jiangsu Academy of Agricultural Sciences (Gu et al. 1994). Questions still remain about the persistence of these hybrids. In recent years, some hybrid pennisetums have displayed yellow leaves and poor tillers at the seedling stage, resulting in stunted plants with low biomass yield. The reason, in part, was that the Correspondence: Xia Zhang, Institute of Animal Science, Jiangsu Academy of Agricultural Sciences, Nanjing, China. E-mail: yangymn@yahoo.com. cn 96 Xia Zhang, Hongru Gu, Chenglong Ding, Xiaoxian Zhong, Jianli Zhang and Nengxiang Xu elephant grass N51, the male parent, was a highly hybrid line. Seeds from selfed progeny of elephant grass N51 were collected and used in the present study. The objectives of the study were to: (1) study the variation within the selfed progeny of elephant grass N51; (2) evaluate the importance of different morphological traits to dry matter yield in elephant grass; (3) determine the direct and indirect effects of these morphological traits on dry matter yield; (4) develop selection criteria for higher biomass yield of elephant grass through the use of path-coefficient analysis; and (5) develop and select improved populations and germplasm of elephant grass for forage and bioenergy production. Materials and methods The trial was conducted during 2007 at Jiangsu Academy of Agricultural Sciences, Nanjing, Jiangsu province (118°48′E, 32°32′N), China. The area has a humid subtropical monsoon climate, with cold winters and hot summers, and a long-term average temperature of 15.7°C and annual precipitation of 1000 mm. The soil was a yellow brown earth, known as magan clay loam in China. The field was fallowed during winter and was ploughed before planting.