Theor Appl Genet (1988) 76:550-554
9 Springer-Verlag 1988
Genetic basis of resistance to zonate leaf spot disease in forage sorghum R. P. S. Grewal Department of Plant Breeding, Haryana Agricultural University, Hisar-125004, India Received October 10, 1987; Accepted March 22, 1988 Communicated by G.S. Khush
Summary. Generation mean analysis was carried out for ten crosses between two resistant and two susceptible parents to find the genetic basic of resistance to zonate leaf spot disease in forage sorghum. In all crosses except one, at least one type of non-allelic interaction was present. Both additive and dominance gene effects were significant for most crosses. Duplicate type epistasis was present for the inheritance of this disease. Resistance to this disease revealed overdominance. Appropriate breeding plans were suggested to exploit the disease resistance.
Key words: Zonate leaf spot - Gloeocercospora sorghi Foliar disease - Alternate breeding
Introduction S o rg h u m is the major fodder crop of northern India and is grown during summer and kharif seasons. Almost all forage sorghum varieties under cultivation in India have been found to be quite susceptible to various kinds of red leaf spot diseases. Zonate leaf spots caused by Gloeocercospora sorghi is a m o n g the most serious diseases of forage sorghum that cause considerable reduction in the yield as well as quality of this crop. N o efforts have been made to improve resistance with regard to any kind of foliar diseases in forage sorghum. It is essential to understand the genetic basis of resistance to any kind of disease to formulate an effective breeding programme. Accordingly, the purpose of the present study was to estimate the gene effects responsible for governing resistance against zonate leaf spots in forage sorghum.
Materials and methods The experimental material consisted of two susceptible (PC-I and JS263) and two resistant ($171 and Sorghum roxburghii)
parents, ten crosses among these four parents and their F2 generations, ten backcrosses with the first parent (B1) and ten backcrosses with the second parent (B2) of each cross. All material, namely 4 parents, 10 Fl's, 10 F2's, and 20 backcrosses, was grown in the experimental research area of forage section during kharif, 1980, in a randomized block design comprising three replications. Backcrosses and Fl's were grown in a single row plot, whereas F2's and parents were grown in 12 rows and 3 rows, respectively, of 4 meters each, at a distance of 30 cm apart. To create more chances for the disease to spread, after every row of experimental material there was one row of each susceptible parent, except in the F2 generation in which these susceptible parental lines were grwon after 6 rows of each F 2. The artificial inoculum prepared from most infected lowest 3 - 4 leaves of growing forage sorghum was also sprayed after irrigating the field at the 25 day and 35 day stages of crop growth to supplement the natural infection. The data were recorded for zonate leaf spots on each leaf of 120 plants in F2's and each leaf of 10 plants in the rest of the generations when the fungal infection was between 70 to 80 days of crop growth on the basis of symptoms given by Williams et aL (1978). Scoring of each leaf was done according to the modified disease rating scale of Scherff (1973). The infection index was calculated according to Wheeler (1969) as Infection Index = sum of individual rating x 100/No. of leaves assessed x number of rating. The data in percentage were subjected to angular transformation for the final statistical analysis. The scaling tests of Mather (1949) and Hayman and Mather (1955), the joint scaling test of Cavalli (1952) and generation mean analysis of Hayman (1958) and Jinks and Jones (1958) were applied for genetic analysis.
Results and discussion Highly significant variation for zonate leaf spots reaction am o n g different generations of various crosses was observed in the present material (Grewal et al. 1986). Such differences am o n g generation means are accounted in terms of estimation of additive and dominance gene effects and non-allelic interactions through generation
551 Table 1. Scaling tests (Mather 1949; Hayman and Mather 1955) for zonate leaf spot (Gloeocercospora sorghi) disease incidence for the ten crosses Sr. no.
Cross
A
B
C
D
1
S. roxburghii x S171
-2.23 * __0.66
- 2.09 ** _ 1.06
0.36 _+1.44
2.34* ___0.48
2
JS263 x PC-1
- 0.43 ___1.48
1.57 _+1.77
- 8.43"
- 4.78"
_ 1.88
+ 1.09
3
S. roxburghii x JS263
- 3.36 ** _ 1.60
- 3.67 ** q- 1.79
- 9.63 * • 1.86
- 1.29 + 1.18
4
S. roxburghii x PC-I
-1.63 _ 1.59
-0.70 + 1.70
-7.04* •
4.69* • 1.11
5
St 71 • JS263
- 2.65 _ 2.01
- 3.28 ___t.80
- I 1.26" + 2.24
6
S171 • PC-1
0.73 _+1.89
6.22" ___1.56 - 3.85 ___2.18
- 17.77" + 1.64
- 4.03 * • 1.31
5.23 ** •
- 2.66 ** + 1.28 -0.86 • 1.19
7
JS263 • S. roxburghii
- 5.85 * _ 1.29
8
JS263 • S171
- 5.62"
- 6.47"
• 1.41
• 1.81
- 11.90" + 1.85
0.09 ___1.22
PC-1 • S. roxburghii
5.51 * • 1.46
1.13 • 1.92
-2.70 • 1.72
-4.67* _+1.24
PC-I • $171
2.87 • 1.67
-0.08 • 1.87
-5.65* + 1.83
-4.22* ___1.23
9 10
* Significant at the 1% level ** Significant at the 5% level
m e a n analysis. Scaling tests of M a t h e r (1949) a n d H a y m a n and M a t h e r (1955) i n d i c a t e d the presence of n o n allelic i n t e r a c t i o n in all the crosses, (Table 1) as one o r the o t h e r scale was significant. T h e significance of C h i - s q u a r e values of Cavalli's (1952) three p a r a m e t e r m o d e l confirmed the presence of such non-allelic interactions (Table 2) a n d i n d i c a t e d t h a t this m o d e l was i n a d e q u a t e to e s t i m a t e gene effects. T h e estimates of a d d i t i v e a n d d o m i n a n c e gene effects are always biased in the presence of epistasis. Accordingly, to k n o w the n a t u r e of epistasis a n d to e s t i m a t e gene effects w i t h o u t bias d a t a were a n a lysed t h r o u g h six p a r a m e t e r m o d e l s as suggested by H a y m a n (1958) as well as Jinks a n d J o n e s (1958). It was interesting to n o t e t h a t in the cross S. roxburghii x JS263, which revealed the presence of n o n allelic i n t e r a c t i o n s t h r o u g h scaling and j o i n t scaling tests, epistasis was a b s e n t w h e n d a t a were analysed t h r o u g h s i x - p a r a m e t e r m o d e l s (Tables 3 a n d 4). Such a situation m a y arise due to the presence of high g e n o t y p e x envir o n m e n t i n t e r a c t i o n s because the estimates of gene effects were n o t biased by linkage since inter-allelic interactions were n o t involved. Thus, for this cross w h e r e epistasis was absent, Cavalli's m o d e l (1952), which revealed the significance of a d d i t i v e as well as d o m i n a n c e gene effects, w o u l d be c o n s i d e r e d fit. T h e results of six p a r a m e t e r m o d e l s revealed t h a t for the cross b e t w e e n resistant • resistant parents, i.e.S, fox-
burghii x S171, o n l y d o m i n a n c e gene effect was significant; w h e r e a s for the cross b e t w e e n susceptible • susceptible parents, i.e. JS263 • P C - I , o n l y additive gene effect was significant. H o w e v e r , in b o t h the cases a d d i t i v e x additive a n d d o m i n a n c e • d o m i n a n c e types of epistasis were present. T h e t w o m o d e l s differed in the case of a cross b e t w e e n susceptible x susceptible parents, as the Jinks a n d J o n e s (1958) m o d e l r e v e a l e d that b o t h a d d i t i v e as well as d o m i n a n c e gene effects were i m p o r t a n t for this cross. T w o m o d e l s also differed for the cross JS263 • S. roxburghii, but in the reverse way, in revealing the result of gene effects. Such discrepancies m a y be attributed, in part, to differences in the e x p e c t a t i o n s of these p a r a m eters in the t w o m o d e l s a n d to the h e t e r o g e n e i t y of the variances of different g e n e r a t i o n s used in this study. T h e results o b t a i n e d using the Jinks a n d J o n e s (1958) m o d e l c o n t r a d i c t e d the H a y m a n (1958) m o d e l with r e g a r d to m e a n (m) values of the t w o crosses PC-1 x S. roxburghii a n d PC-1 • with n e g a t i v e m e a n values in the f o r m e r m e t h o d that s h o u l d n o t be t h e o r e t i c a l l y so. H o w ever, u n e x p e c t e d results m a y be due to s a m p l i n g error. M o r e o v e r , these n e g a t i v e values w o u l d n o t affect the overall e s t i m a t i o n of results as they were non-significant. All the crosses b e t w e e n resistant x susceptible a n d susceptible x resistant parents, except S171 • JS263, S171 x PC-1 and JS263 • S171 in w h i c h o n l y a d d i t i v e gene effects with either T o r 'j' o r T type of epistasis was
552 Table 2. Estimates o f j o i n t scaling test (Cavalli 1952) for the ten crosses for zonate leaf spot (Gloeocercospora sorghi) disease incidence Sr. no.
Cross
m
d
h
X2
1
S. roxburghii • S171
1.08 +0.29
-0.25 +0.30
0.42 +0.59
8.45*
2
JS263 • PC-1
16.86 _+0.37
5.61 * ___0.38
-7.10" +0.73
31.45"
3
S. roxburghii x JS263
11.22 -+0.32
- 10.99" -t-0.33
- 5.92 * -+0.65
26.92"
4
S. roxburghii x PC-1
6.62 -+0.33
-5.81 * ___0.33
1.35 +0.70
23.53*
5
S171 x JS263
11.76 -+0.37
- 10.65 * _+0.38
- 2.48 * ___0.79
25.90"
6
S171 x PC-1
7.41 +0.37
-5.57* +0.38
2.38* +0.75
16.95"
7
JS263 x S. roxburghii
10.22 _+0.30
10.51 * -t-0.32
1.11 +0.58
117.34"
8
JS263 x S171
11.08 _+0.35
10.58" ___0.37
0.03 -+0.63
49.63*
9
PC-1 • S. roxburghii
6.42 +0.31
5.99* _+0.33
2.67* -+0.60
24.84*
PC-1 • S171
6.42 +__0.38
5.28* _+0.38
2.27* _+0.70
19.78"
10
* Significant at the 1% level
Table 3. Estimates of gene effects for zonate leaf spot (Gloeocercospora p a r a m e t e r model of H a y m a n (1958) Sr. no.
Cross
m
d
sorghi) disease incidence in the ten crosses using the six
h
i
j
1
1
S. roxburghii x S171
1.48 +0.16
-0.62 +0.36
-4.34* + 1.16
-4.69* +0.96
-0.07 +0.49
2
JS263 x PC-1
12.41 +0.25
4.64* ___0.96
3.50 ___2.32
9.57* + 1.18
-1.00 _ 1.05
3
S. roxburghii x JS263
7.43 ___0.27
- 11.11 * + 1.05
- 1.57 __+2.49
2.59 ___2.37
0.15 ___1.10
4.44 + 4.60
4
S. roxburghii • PC-1
8.16 +0.27
-6.08* +0.96
-9.15" +2.39
-9.38* +__2.22
-0.46 ___1.03
11.72" ___4.37
5
$171 x JS263
9.64 + 0.29
- 10.39 * _ 1.13
5.27 + 2.73
5.32 ** + 2.56
0.31 + 1.20
0.60 _+5.07
6
S171 • PC-1
8.82 ___0.29
-7.81 * + 1.03
3.07 -+ 2.53
1.73 _ 2.39
-2.74** _ 1.11
7
JS263 x S. roxburghii
8.60 -t-0.29
10.26" + 1.17
10.30" +2.66
8.07" +2.62
- 0.99 _ 1.22
_ 4.97
9.03 * _ 2.03 -
10.71 ** + 4.29
8.69 ___4.62 -
1.63
8
JS263 x S171
9.81 +0.33
11.13" _ 1.01
0.42 +2.52
-0.19 _ 1.09
0.42 _ 1.09
12.29" _+4.47
9
PC-1 • S. roxburghii
7.05 ___0.29
7.81 * + 1.69
12.22" +2.55
9.34* +2.41
2.18 + 1.15
- 15.99" __ 4.70
PC-1 x S171
6.28 +0.27
6.55* _ 1.10
11.23" +2.56
8.44* -t-2.46
1.48 + 1.18
-11.22"* ___4.78
10
* Significant at the 1% level ** Significant at the 5% level
553 Table 4. Estimates of gene effects for zonata leaf spot (Gloeocercospora sorghi) disease incidence in the ten crosses using the six parameter model of Jinks and Jones (1958) Sr. no.
Cross
m
d
h
1
S. roxburghiixSl71
5.91 _ 2.24
-0.55 ___0.34
2
JS263 • PC-1
7.98 + 2.22
5.64* _+0.42
3
S. roxburghii x JS263
9.33 ___2.40
4
S. roxburghii x PC-1
5
j
1
-4.69** ___2.22
-0.14 _+2.23
9.03** + 4.48
14.22"* ___6.30
9.57* ___2.18
-2.00 _ 2.10
-10.71 ** _ 4.29
- 11.26 * _ 0.35
- 6.02 ___6.80
2.59 _ 2.37
0.30 _+2.21
4.44 ___4.60
15.67 + 2.25
- 5.62" __+0.36
- 20.87" ___6.34
- 9.38" _ 2.22
- 0.92 ___2.06
- 11.72" _+4.37
S171 x JS263
7.15 _+2.60
- 10.71 * _ 0.40
4.66 _ 7.38
5.32 ** _ 2.56
0.63 + 2.41
0.60 _ 5.07
6
$171 x PC-1
5.11 _ 2.43
-5.07* + 0.41
11.76 _ 6.81
1.73 ___2.39
-5.49** + 2.23
-8.69 ___4.62
7
JS263 • S. roxburghii
3.85 ___1.84
11.26" _ 0.35
8.67 + 7.51
8.07 * _ 2.62
- 1.99 + 2.45
1.63 __+4.97
8
JS263 x $171
12.67 __2.47
10.71 * ___0.40
- 11.86 ___6.81
-0.19 +2.44
0.84 ___2.19
12.29" ___4.47
9
PC-1 x S. roxburghii
- 3.05 + 2.50
5.62* ___0.36
28.21 * _ 7.06
9.34* + 2.48
4.37 _ 2.30
- 15.99" _ 4.70
PC-1 x $171
- 1.59 _ 2.49
5.07* _ 0.41
22.46* ___7.11
8.44* _ 2.46
2.96 ___2.36
- 11.22" ___4.78
10
-13.37"* ___6.61
i
* Significant at the 1% level ** Significant at the 5% level
significant, r e v e a l e d t h e significance o f b o t h a d d i t i v e • additive and dominance x dominance interactions. Magn i t u d e o f d o m i n a n c e g e n e effects w a s also h i g h e r in s u c h crosses. V a r i a t i o n in t h e significance o f g e n e t i c a l p a r a m e ters i n r e c i p r o c a l crosses m a y b e a s c r i b e d to s a m p l i n g error.
C o m p a r i s o n s o f signs ( n e g a t i v e or positive) of t h e d o m i n a n c e g e n e effects (h) a n d d o m i n a n c e x d o m i n a n c e i n t e r a c t i o n (1) p a r a m e t e r s in crosses w h e r e b o t h t h e s e p a r a m e t e r s w e r e s i g n i f i c a n t r e v e a l e d d u p l i c a t e t y p e s of g e n e i n t e r a c t i o n s (as t h e signs of t h e s e t w o p a r a m e t e r s were opposite), c o n f i r m i n g t h e i m p o r t a n c e of d o m i n a n c e g e n e effects a l o n g w i t h a d d i t i v e g e n e effects i n t h e i n h e r i t a n c e o f z o n a t e leaf s p o t disease resistance. R a n a et al. (1982), i n v e s t i g a t i n g t h e i n h e r i t a n c e of s o r g h u m d o w n y m i l d e w resistance, also r e p o r t e d t h e p r e s e n c e of a d u p l i c a t e t y p e of i n t e r a c t i o n . T h e p o t e n c e r a t i o [h]/[d], w h e r e b o t h ' h ' a n d 'd' p a r a m e t e r s were significant, r e v e a l e d t h e d e g r e e of d o m i n a n c e t o b e o v e r - d o m i n a n c e , i n d i c a t i n g m o r e i m p o r t a n c e o f d o m i n a n c e g e n e effects w i t h r e g a r d to this disease resistance. In such situations the most suitable breeding plan w o u l d b e o n e t h a t m o p s u p t h e a d d i t i v e g e n e effects a n d at the same time maintains appropriate heterozygosity for h a r n e s s i n g t h e i n t e r a c t i o n effects. A n a l t e r n a t e b r e e d i n g a p p r o a c h a n d a s y s t e m of r e c u r r e n t s e l e c t i o n gives
m a x i m u m o p p o r t u n i t y for r e a r r a n g e m e n t o f g e n e s a n d c a n raise t h e g e n e t i c ceiling o f t h e c o n c e r n e d p o p u l a t i o n by accumulating favourable additive genes through interc r o s s i n g t h e selects, a n d h e n c e c o u l d p r o v e t o b e t h e m o s t appropriate. Reciprocal recurrent selection seems to be m o r e effective in utilizing b o t h a d d i t i v e a n d d o m i n a n t g e n e effects a n d t h e o r e t i c a l c o n s i d e r a t i o n s i n d i c a t e t h a t t h e p r e s e n c e of n o n - a l l e l i c i n t e r a c t i o n s w o u l d f a v o u r rec i p r o c a l r e c u r r e n t s e l e c t i o n as c o m p a r e d w i t h r e c u r r e n t s e l e c t i o n for g e n e r a l c o m b i n i n g ability. F o r t h e crosses w i t h d u p l i c a t e t y p e s of epistasis a s s o c i a t e d w i t h signific a n t a d d i t i v e g e n e effects, p e d i g r e e a n d b a c k c r o s s b r e e d ing w o u l d b e helpful t o a c c u m u l a t e t h e r e q u i r e d resistance.
Acknowledgements. Thanks are due to the Haryana Agricultural University, Hisar for granting the study leave, to the Council of Scientific and Industrial Research, New Delhi for granting financial help in the form of Senior Research Fellowship, to Dr. G.P. Lodhi, Senior Breeder (Sorghum) and to Dr. R.S. Paroda, Director, N B P G R , for their guidance during the course of this investigation.
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