Applied Science and Biotechnology Journal for Advanced Research

Introduction

Rhodes grass is one of the perennial improved grass which can be grown on-farm and used by small-holder farmers (Arshadet al., 2020). It is high-yielder, fast growing, palatable and deep rooted grass which grows under a wide range of environmental conditions and is useful in cut-and-carry system and for open grazing and is very popular for hay making. It does well in low rainfall areas and is drought tolerant; stands heavy grazing and cutting; very palatable. Rhodes grass is very palatable and has good nutritive value and has high protein content (9-12 %) with an average water intake of about 600 mm to 1200 mm. Sowing Rhodes grass for more than three years gives rise to development (Arshadet al., 2016).

Due to its deep roots, it can withstand long dry periods (over 6 months) and up to 15 days of flooding. It grows well on a drained moderate to high fertility soils and survives on infertile soils although it is unproductive and may eventually die out particularly if grazed regularly. Rhodes grass is a full sunlight species, which does not grow well under shady environments (FAO, 2014 and Ecocrop, 2014).Growth performance of Rhodes grass varies with type of cultivar, age of plant and other environmental factors (FAO, 2009). Rhodes grass productivity generally ranges from 7 - 25 tons of DM ha-1 per year, depending on variety, soil fertility, environmental conditions and cutting frequency. However; there is only one variety of Rhodes grass in Ethiopia which was released by Holota Agricultural Research Center in 1984 and accepted by huge farmer and private farms.

The productivity of the forage is low due to many limiting factors such as shortage of adapted high yielding varieties, using unknown seed sources and poor-quality seeds, lack of genotypes. Diversity studies are an essential step and pre-requisite in forage breeding and could produce valuable knowledge for forage improvement programmers. The presence of genetic variability in forage is essential for its further improvement by providing options for the breeders to develop new varieties and hybrids. Hence, generating information on the degree and pattern of genetic diversity of the Rhodes grass genotypes were less/no evaluated scientifically using either molecular or morphological studies in Ethiopia.

Sowing was done by drilling the seed in the furrow (line) at depth of 1-2 cm with the seed rate of 12kg/ha. It was sown on well prepared seed bed and sowing similar to that of teff. Then the seed was covered with thin soil by over passing light sticks and fingers over the furrows. 100kg/ha of NPS fertilizer was applied at the time of sowing and 50kg/ha Urea after establishment. Before Sowing, appropriate experimental site was be selected, ploughed and leveled for ease of layout and managements. All managements were applied uniformly for all genotypes at necessary time.

Data Collected

Data Collected: quantitative characters on recorded on five randomly selected plants from the two middle rows of each plot.

Growth: The developmental process such as days to emergence, days to 50% flowering and maturity stage will be recorded.

Plant Height (cm): The average plant height will be measured from ground to the tip of the main stem. The measurement will be done by taking ten random plants at 50% flowering stage from the two middle rows of each plot.

Number: Counts of plant number, number of leaves per plant and number of tillers per plant will be recorded at 50% flowering stage. Ten plants from each plot in a quadrant (0.25m2) will be taken to measure number of tillers per plant, number of leaves per plant and number of leaves per tiller. Average results from each measurement will be recorded to evaluate the performance (Aklilu, 2007).

Biomass Yield: The vegetation from each plot will be sampled using a quadrant of 0.25m2 (0.5m x 0.5m) sizes during a predetermined sampling period (50% flowering stage). The quadrant will be randomly thrown on a plot and the average weight from the quadrant will be used to determine the biomass yield. The average weight of the fresh fodder will be used and extrapolated into dry matter yield per hectare (t/ha). Three adjacent rows from the center of each plot will be taken at 50% flowering stage for fodder yield evaluation (Aklilu, 2007). The fresh harvested biomass will be chopped into small pieces using sickle and a sub-sample of 250 g was taken and partially dried in an oven at 60 ˚C for 48hrs for further dry matter analysis.

Estimation of Genetic Advance and Broad Sense Heritability

Genetic Advance under Selection (GA) is expected genetic advance for different characters under Selection was estimated using the formula suggested by Lush and Johnson (1955).

Where, Vp=Phenotypic standard deviation, GA=Expected genetic advance and k=the standardize selection differential at 5%

selection intensity (K=2.063). Genetic advance as percent mean was categorized as low (0-10%), moderate (10-20% and (≥20%) as given by Johnson et al., 1955 and Falconer and Mackay (1996).

Broad Sense Heritability (H2b): Heritability in broad sense (H2b) was estimated according to the formula suggested by Johnson et al., 1955 and Hanson et al., 1956.

Where, H²b=Heritability in broad sense, VG=Genotypic variance, VP=Phenotypic variance. The heritability was categorized as low (0-30%), moderate (30- 60%) and high (60% and above) as given by Robinson et al., 1949.

Results and Discussions

Analysis of Variances

The mean sum of squares of genotypes showed significant differences (p < 0.05) for stand vigor, 50% emergence date, 50% Flowering date and Plant height and highly significant (p < 0.001) for biomass yield, dry matter and number of tiller per plant (Table 1). Indicates that there was ample scope for selection of promising genotypes for yield improvement. Highest values were estimated for plot cover followed by Plant height, days to 50% flowering, fresh biomass yield, days to 50% emergence and Dry matter yield.The wide range of variation observed in 81% of characters offers scope of selection for different quantitative traits of Rhodes grass.

Estimation of Variance Components

The estimates of variance, coefficient of variation, heritability and genetic advance for all eleven characters studied are presented in table 3. Maximum (VP) value was recorded for days to maturity, plot cover, plant height and leaf to stem ratio, 508, 341.7, 130.7 and 128.5respectively. Similarly, (Vg) value for these characters were also high indicating for days to mature, days to 50% flowering and plot cover, 80.7, 38.8, 28.5 and 15.1respectively. Also Maximum (Ve) value was recorded for days to maturity, plot cover, leaf to stem ratio and plant height 427.3, 326.7, 127 and 91.9 respectively.Less difference in estimates of genotypic and phenotypic variance and higher genotypic values compared to environmental variance for all characters suggested that variability present among genotypes were mainly due to genetic reason with minimum influence of environment and hence heritable (Abdul et at., 2017). The estimates of heritability are more advantageous when expressed in terms of genetic advance Johnson et al. (1955). The range observed for heritability (H²bs) was from (0.0%) to (55%). The moderate heritability were recorded for number of leaf per plant (55%), days to 50 % flowering (42.3%), days to 50% emergence (30.8%), stand vigor (31.3%). The rest of traits were grouped in low values of heritability. Genetic advance as percentage of mean ranged from 0% to 30.2% stand vigor and seed yield respectively (Table 2). Stand vigor exhibited highest value of genetic advance as percentage of mean (30.2%) while number of leaf per plant (18.4%) and days to 50% emergence (13.2%) where exhibited moderate value of genetic advance as percentage of mean.All rest traits recorded lowest value during observation.

Table 3:Estimation of genetic parameters for 10 Traits in 24 Rhodes genotypes and one check varieties

Table 4:Genotypic (above diagonal) and phenotypic (below diagonal) correlation coefficients among 10 traits studied at Mechara Agricultural Research on station

Plot Cover

Plot cover exhibited significant positive phenotypic correlated with stand vigor (0.873**), Leaf to stem ratio (0.421**), Plant height (2.527**), Number of Leaf per Plant (0.441**), Days to 50% flowering (-0.499*) were showed negatively significant while seed yield (0.098NS)showed positive non-significant,however, non-significant positive relationship was observed with days to maturity.Genotypic relationship of Plot cover was highly significant with stand vigor (1.4661**), Leaf to stem ratio (6.656**), Plant height (2.527**), Number tiller per plant (1.561**), Dry Matter yield (1.621**), while the genotypic correlation was negative with days to 50% emergence (-1.229**) and seed yield (-6.374**).

Days to Maturity

Least days to maturity in forage harvest is the best indication for a desirable variety, because it contracts forage duration. Genotypic correlation for days to reach physiological maturity was highly significant positive correlated with Plot cover (0.886**), stand vigor (0.488*), Leaf to stem ratio (1.301**), Plant height (0.674**).

Phenotypically it was non-significantly positively correlated with, plot cover (0.099) stand vigor (0.1297), Leaf to stem ratio (0.219), and Days to 50% emergence (0.212).

Stand Vigor

Stand Vigor shown highly positive phenotypic co-relationship with dry matter yield (0.566**), leaf to stem ratio (0.449**), Tiller number (0.412**) and Plot cover (1.4661**) but positively non-significant correlation with days 50% flowering, days to maturity and seed yield. Genotypically stand vigor showed high significant positive linkage with leaf to stem ratio (6.656**), days to 50% flowering (0.808**), Plant height (2.527), number of tiller (1.561**), days to maturity (0.886**) and Dry matter yield (1.621**), whereas, significant negative linkage was exhibited with days to 50% emergence (-1.229**) and seed yield (-6.374**).

GenotypicPathCoefficientAnalysisofDry Matter YieldwithOtherTraits

The results of genotypic path coefficient analysis of drymatteryieldwithother9 traits are presented in (Table 5). Accordingto Muchero et al., (2008) who classified path coefficients(0.00-0.09)negligible,(0.10-0.19)low (0.20 - 0.29) moderate, and (0.30 - 0.99) high and more than 1.00 is very high.In the present investigation, stand vigor followed by plant height, plot cover and leaf per plant had exerted high and positive direct effect on dry matter yield, also leaf per plant and seed yield had exerted moderate and neglible positive direct effect on dry matter yield. However, leaf to stem ratio, days to 50% emergence, days to 50% flowering, days to maturity had exerted negative direct effect on dry matter yield.

Table 5: Genotypic path coefficient analysis for direct (bold diagonal) and indirect effect (off diagonal) 9 traits studied on Rhodes grass dry matter yield

The mean sum of squares of genotypes showed significant differences for most traits. Maximum phenotypic variance and genotypic variance value was recorded for days to maturity. The range observed for heritability (H²bs) was from (0.0%) to (55%). Stand vigor exhibited highest value of genetic advance as percentage of mean followed by number of leaf per plant. Highest genotypic coefficient variation were recorded from days to maturity flowed by Plant height and Highest phenotypic coefficient variation were recorded from plot cover followed by days to maturity. Phenotypically and Genotypically dry matter yield was highly positive significant associated with of Plot cover, stand vigor, leaf per plant and showed highly negative significant with days to emergence. Phenotypic path coefficient analysis showed that stand vigor and leaf per plant had exerted moderate positive direct effect on dry matter. Stand vigor followed by plant height, plot cover and leaf per plant had exerted high and positive direct effect on dry matter yield and genotypicpathanalysis showed stand vigor followed by plant height, plot cover. Therefore, selection based on high biological biomass yield and leaf per tiller together with the above indicated traits is recommended for further dry matter yield improvement of Rhodes grass if selection will be done for individual different location.

References

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