99 iii. genes with additive effects control stem brix, stem biomass and associated traits in
sorghum, and
iv. genes with non-additive effects control stem brix, stem biomass and associated traits in sorghum.
100
Table 5.3-1: Name, origin and pedigree of parental sorghum lines used in the study Line
No.
Name Fertility status
Origin Pedigree Role in
crosses
1 ZLR1 † CMF Zimbabwe Landrace Male
2 MRL15 CMF - Unknown Male
3 ICSV700 CMF ICRISAT India (IS 1082 x SC 108-3)-1-1-1-1-1 Male 4 ICSVP3046 CMF ICRISAT India (ICSV 700 x ICSV 708)-9-1-3-1-1-1 Male
5 S35 CMF ICRISAT India - Male
6 Macia CMF Mozambique SDS 3220 Male
7 ZLR2 CMF Zimbabwe Landrace Male
8 ICSR165 CMF ICRISAT India SPV 422 Male
9 ICSR57 CMF ICRISAT India (SC 108-3 x 148)-12-5-3 Male
10 Thar CMF - - Male
11 ICSA731 CMS ICRISAT India ICSV 1171BF Female
12 ICSA479 CMS ICRISAT India [9ICSB 70 x ICSV 700) x PS 19349B]-5-4-1-2-2 Female 13 ICSA4 CMS ICRISAT India [(BTx 622 × UChV2)B lines bulk]-10-1-1 Female
14 ICSA724 CMS ICRISAT India ICSP 1B/R MFR-S 7-303-2-1 Female
15 ICSA307 CMS ICRISAT India [(ICSB 26 × PM 1861)×(ICSB 22 × ICSB 45) × (ICSB 52 × ICSB 51)]1-3-12-3-1
Female 16 ICSA474 CMS ICRISAT India (IS 18432 x ICSB 6)11-1-1-2-2 Female 17 ICSA26 CMS ICRISAT India [(296B x BTx 624)B lines bulk]-2-1-1-3 Female 18 ICSA623 CMS ICRISAT India (ICSB 11 x PM 17467B)5-1-2-1 Female Introduced checks
Saccaline CMF USDA -
Grassl CMF USDA -
† = local check; CMF = cytoplasmic male fertile; CMS = cytoplasmic male sterile; - = unknown pedigrees
5.3.2 Experimental sites
The experiment was conducted at Chokwe Research Station (CRS) (24° 31′ S; 33° 0′ E, 40m.a.s.l) in Mozambique and at Makhathini Research Station (MRS) (27º 24’S; 32º 11’ 48”
E, 72m.a.s.l.) in South Africa during off-season (May to September 2008) and in-season (November 2008 to April 2009). Further in-season trials were conducted at Rattray-Arnold Research Station (RARS) (17º 40’ S; 31º 14’ E, 1308m.a.s.l.) in Zimbabwe and at Ukulinga Research Farm (URF) (30º 24’ E; 29º 24’ E, 781m.a.s.l.) in South Africa during November 2008 to April 2009. Both CRS and MRS represent the tropical lowland environments in southern Africa where there is potential for sorghum production both in-season and off- season without adverse effects of low temperatures. The two sites have annual long term
101 mean rainfall of about 600mm and maximum temperatures of about 25-300C (Figure 5.3-1).
RARS and URF represent the mid-altitude environments with annual rainfall of about 800mm and maximum temperatures of 20-300C (Figure 5.3-1). Although the rainfall is seasonal at all sites, the temperatures and availability of irrigation facilities at CRS and MRS make them ideal for sorghum production throughout the year, unlike URF and RARS where low winter temperatures make it impossible to grow cold sensitive crops like sorghum during May to September. Both CRS and MRS are surrounded by small-scale irrigation schemes with perennial water sources.
Mean temperature (ºC)
Month
Figure 5.3-1: Long term mean (five-year) temperatures for CRS, URF, RARS and MRS [Data source:
Agricultural Research Council-ISCW AgroMet Potchefstroom (2009); Seed Co. Zimbabwe Ltd (2009);
Gaisma (2007)]
5.3.3 Experimental design and management
The experiments were laid out as replicated row-column α-designs at each site during May of 2008. Seeds of each entry were planted by hand in two-row plots of 3.0m length at 0.75m inter-row and 0.20m intra-row spacing resulting in a population density of about 66 667 plants ha-1. At MRS and URF, the experiment was laid as a 10 rows × 10 columns and at CRS and RARS, it was a 5 rows × 20 columns. The trials were supplied with 800mm moisture through irrigation during off-season and by supplementary irrigation during in-season. The trials were supplied with 250kg ha-1 basal fertiliser (2:3:4, N:P:K) and 200kg ha-1 top dressing fertiliser (Lime Ammonium Nitrate with 28% N). The fields were kept weed free by hand weeding. At planting, Curaterr 5G (carbofuran), a systemic insecticide, was applied to prevent damage of
10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0
Jan Feb March Apr May June July Aug Sept Oct Nov Dec
CRS URF RARS MRS
102 the emerging seedlings by mice and cutworm. Stalkborer granules (dimethyl-(2,2,2-trichloro- 1-hydroxyethyl) phosphonate) were used to control stalkborer damage and the sorghum heads were covered using fine mesh bags at anthesis to prevent bird predation on the developing grain.
Stem sugar concentration was measured in brix, using an Atago PAL-1 digital hand-held pocket refractometer (with automatic temperature compensation ranging from 0 to 50°C) at the hard dough stage. Due to differences in maturity, each entry was harvested separately when it reached the hard dough stage. The stems were divided into three equal parts, top, middle and bottom sections, and three brix measurements were taken using the middle internode of each section. Stalk juice was squeezed from the cut internode section into the sample stage of the refractometer using a pair of pliers. Both the pliers and the refractometer sample stage were rinsed with clean water and dried with tissue paper before the next sample was measured to contamination with stalk juice from previous samples. Stem diameter and stem juiciness score were also measured from the three mid internode sections using a veneer calliper and a rating scale of 1 (juicy) to 9 (dry) depending on the ease of pressing and resultant juice pressed, respectively. The final values for stem brix, diameter and juice score were an average of the three measurements. Juiciness was scored because of the absence of juice extractors that would assist in the quantification of total amounts of juice per stalk weight. In the absence of juice extractors, breeders risk discarding good materials if selection is based on the refractometer reading alone. To address this problem, an index, the ‘stem °brix-juice index’ was calculated as follows:
Stem brix-juice index = brix ÷ log [juice score + 1]
Given the same brix reading, this calculation results in an upward adjustment of juicy cultivars over dry ones because at equal brix readings, juicier cultivars have more sugar compared to drier ones. With this index, total sugar becomes a function of stem biomass per unit area. At a given biomass yield, cultivars with high indices are selected over those with lower indices.
Stem biomass was measured at the hard dough stage by stripping plants of all leaves and heads, then cutting at ground level and weighing the stems. Plant height was measured using a 3.0m ruler. Number of days to 50% flowering (time in days taken for half of the plants in a plot to reach anthesis) and days to 95% physiological maturity (time in days to the stage when about 95% of the plants have reached the hard dough stage) were also measured by visual inspection.
103 5.3.4 Data analyses
Data were analysed using REML procedure in GenStat® (Payne et al., 2007) following a fixed effects model:
Yijkl = µ + si + rj(si) + b(rj*si) + mk + fl + mfkl + si*mik+ si*fij +s*mfikl + eijkl
Where: Yijk = observed hybrid response; µ = overall population mean; si = effect of the ith environment; rj(si) = effects of the jth replication in the ith environment; b(rj*si) = effects of the blocks in the jth replication in the ith environments; mk = effect of the kth male parent; fl = effect of the lth female parent; mfkl = interaction effect of the kth male and the lth female parents; si*mfkl
= interaction effect of the ith environments and the interaction effects between the kth male and the lth female parents; and eijkl is the experimental error.
The hybrid variation was partitioned into male and female parent main effects giving two independent estimates of GCA effects, while the male × female interaction estimates the SCA effects (Hallauer and Miranda, 1988; Kearsey and Pooni, 1996). The GCA effects for the parents were calculated according to Kearsey and Pooni (1996) as follows:
GCAf = Xf – µ and GCAm = Xm – µ, Where: GCAf and GCAm = GCA of female and male parents, respectively; Xf and Xm= mean of the female and male parents, respectively; µ = overall mean of all crosses.
The standard error (SE) and standard error of a difference (SED) for male and female GCA effects were calculated according to Dabholkar (1992) separately because the numbers of males and females were not balanced as follows:
SEmale = √(MSE/s*r*f), SEfemale = √(MSE/s*r*m) and SEDmale = √(2MSE/s*r*f), SEDfemale
= √(2MSE/s*r*m), Where: MSE = mean square error; r = number of replications; f and m = number of female and male parents, respectively.
The SCA effects of the crosses were computed according to Kearsy and Pooni (1996) as follows:
SCAX = XX - E(XX) = XX – [GCAf + GCAm+ µ], Where: SCAX = SCA effects of the two parents in the cross; XX = observed mean value of the cross; E(XX) = expected value of the cross basing on the GCA effects of the two parents;
GCAf and GCAm = GCA of female and male parents, respectively.
The standard error (SE) and standard error of the difference (SED) for the SCA effects were calculated according to Dabholkar (1992) as follows:
104 SE = √(MSE/r) and SED = √(2MSE/r), Where: MSE = mean square error; r = number
of replications.
Better parent heterosis (%) was computed according Alam et al. (2004) as follows:
Better parent heterosis (%) = [(Xx – XBP)/XBP]*100%,Where: XX = observed mean value of the cross; XBP = mean of the better parent.
Standard heterosis was computed according to Kaushik et al. (2004) as follows:
Standard heterosis (%) = [(XE)/XSC]*100%, Where: XE = observed mean value of the entry; XSC = mean of standard check.
Stability of the entries across the environments was measured by the cultivars general superiority index (Pi) calculated in excel in accordance with Lin and Binns (1988) as follows:
Pi = Y −M /(2n)
Where: n = number of locations; Yij = the yield of the ith cultivars in the jth environment;
Mj = the maximum yield recorded in the jth environment
The Pi were computed both per se and inter se for the sorghum parents to determine their stability as pure lines and in hybrid combinations, respectively. The entries that were not represented in all the environments had their Pi computed across those environments in which they were grown. A further parameter, P(is – ps), was devised and computed as the difference between the parental performances inter se minus its performance per se to compare their performance in hybrid crosses against their performance as pure lines.
Therefore, positive P(is – ps) indicate that a genotype was superior in cross combinations than as pure lines and vice versa.