Maize Genetics Cooperation Newsletter vol 81 2007
Maize,
though widely considered a warm weather crop, is currently grown between 550 north
and south latitudes (Shaw, In Corn and Corn Improvement, ASA, Madison, WI,
1988). However, due to a limited
frost-free season, earliness assumes a considerable significance in tailoring
maize cultivars suitable in high altitude areas.
Ten inbred lines, namely PMI-1, PMI-26, PMI-47, PMI-53, PMI-83, PMI-135, PMI-198, PMI-199, PMI-224 and PMI-401 (designated as P1 to P10), were evaluated in a half diallel mating design to generate 45 F1 crosses. The parents and their crosses were evaluated at two locations: the High Altitude Maize Research Sub Station, Pahalgam (2222m asl;341/20N,741/20E) and the Regional Research Station of Sher-e-Kashmir University of Agricultural Sciences and Technology in Khudwani (1542m asl;341/20N,741/20E), Kashmir, India during Kharif 2005. The experimental material was arranged in a randomized complete block design with three replications per location. Lines and crosses were randomized separately in each experiment. Each entry was represented by two rows of 4m length with a crop geometry of 60 x 20cm and a plant density of 83333 plants per hectare. The data were recorded and analyzed for six quantitative traits (Table 1). Grain yield was calculated using fresh ear weight at harvest, assuming 80% shelling and adjusted to 15% moisture content. Ear height was recorded for the primary ear. Combining ability analysis was performed using Griffing�s (Aust. J. Biol. Sci. 9:463-493, 1956) method 2 model II. Pooled analysis over environments was carried out following Singh (Indian J. Genet. 33:469-481, 1973; Indian J. Genet. 39:383-386, 1979)
Pooled analysis of variance for combining ability (Table 1) revealed the presence of highly significance of mean squares due to GCA and SCA for all the characters studied indicating thereby the differences among parental lines for GCA and among crosses for SCA effects. The diversity of test locations was revealed by their highly significant mean squares. Both GCA and SCA effects showed significant interaction with location for all traits. This suggested the differential response of lines and crosses for GCA and SCA effects, respectively, implying thereby that different parental lines are needed to synthesize hybrids for different ecological situations. The SCA effects for grain yield , 50% silking, plant height and ear placement were relatively stable over locations as indicated by lower estimates of SCA x location interaction, whereas the reverse was the case for days to pollen shed and moisture content. The ratio of estimated GCA to SCA variances indicated the preponderance of the latter component in controlling the expression of all traits.
Table
1. Pooled
analysis of variances for different traits in a diallel cross of maize.
|
Source
of variation |
Df |
Grain
yield per plot (Kg) |
Days
to 50% pollen shedding |
Days
to 50% silking |
Moisture
content (%) |
Plant
height (cm) |
Ear
placement (cm) |
|
|
Mean squares |
||||||
|
Locations |
1 |
0.76** |
0.13** |
0.13** |
0.22** |
0.49** |
0.44** |
|
GCA |
9 |
0.87** |
0.75** |
0.44** |
0.32** |
0.70** |
0.89** |
|
SCA |
45 |
0.86** |
0.18** |
0.19** |
0.24* |
0.45** |
0.58** |
|
GCA x Locations |
9 |
0.66** |
0.28** |
0.87** |
0.30** |
0.46** |
0.38** |
|
SCA x Locationst |
45 |
0.13 |
0.30** |
0.30** |
0.45** |
0.14 |
0.11 |
|
Pooled error |
108 |
0.18 |
0.05 |
0.04 |
0.08 |
0.13 |
0.14 |
|
σ2s/ σ2g |
|
0.021 |
0.353 |
0.127 |
0.065 |
0.080 |
0.075 |
*,**significant at 5% & !% level respectively
GCA =
general combining ability
SCA =
specific combining ability
The perusal of GCA effects (data not shown) reveals that P10 was an ideal general combiner for all characters followed by P1, whereas P9 was a good general combiner for all traits except pollen shed. P4, though a good combiner for grain yield, showed positive significant GCA effects for moisture content and plant height. P8 x P9 is the most desirable cross combination for SCA effects, closely followed by P6 x P10 and P8 x P10. An important inference that can be drawn from these results is that cross combinations involving P10 as one of the parents recorded desirable SCA effects for all or most of the traits studied. P10 thus could serve as a potential donor for all these desirable attributes, and therefore has a special value in the maize improvement programme of the high altitude temperate ecology of Kashmir.
Please Note: Notes submitted to the Maize Genetics Cooperation
Newsletter may be cited only with consent of authors.