3.3 Results
3.3.1 Variation in traits in response to site, season, genotype and spray treatment
The effects of genotype x site were highly significant (P<0.001) for most traits (Table 3.2). The AUDPC increased across the seasons at Kachwekano (Figure 3.1a), while the AUDCP peaked in 2011B at Namulonge. As expected, the trend for yield was the reverse to that of AUDPC (Figure 3.1b). At Namulonge and Kachwekano, the yield was lowest in 2010B which coincided with the highest AUDPC. Generally, the HI was low when the disease severity was high (Figure 3.1c). Weevil damage was highest at Namulonge for all the seasons, and was lowest during season 2011B at both sites (Figure 3.1d).
As the four way interaction of genotype x spray treatment x site x season was not significant (P>0.05) for the traits considered (Table 3.2), the trends rather than significant differences between means thereof are discussed for AUDPC and TRY only. These two traits were the main focus of this study and are therefore discussed in detail. The AUDPC values for the genotypes were higher at Kachwekano than at Namulonge for both spray treatments and in all seasons (Table 3.3). At both sites, the highest disease severity for the genotypes was recorded in season 2011B. Across seasons and sites, Shock had lower AUDPC values of 95.3 and 43.0 with the Alternaria inoculation and fungicide treatments, respectively than the resistant check, Tanzania. NASPOT 11 was the third most resistant genotype with a mean AUDPC value of 104.6 when inoculated but with higher AUDPC values at Namulonge than at Kachwekano.
NASPOT 1, the susceptible check, had the highest mean AUDPC values of 162.3 and 96.1 with inoculation and fungicide treatment, respectively. In addition to NASPOT 1, New Kawogo (145.4), Dimbuka (137.8) and NASPOT 7 (136.6) were the most susceptible when inoculation with the disease. Correspondingly, they had higher AUDPC values when sprayed with fungicide.
Fungicide treated plots recorded higher TRY than the inoculated plots (Table 3.4). NASPOT 8 was the highest yielder with means of 17.1 and 21.9 t ha-1 under Alternaria inoculation and fungicide treatments, respectively. NASPOT 11 was the second highest yielder with mean yield of 14.2 and 19.2 t ha-1 under Alternaria inoculum and fungicide treatments, respectively.
NASPOT 7 was the third highest yielder with mean TRY of 12.7 and 17.2 t ha-1, for the same respective treatments. At Namulonge, the highest mean TRY of 14.5 and 20.1 t ha-1 were obtained during season 2011A for the inoculation and fungicide treatments, respectively, while the lowest mean TRY were recorded during season 2010B for both spray treatments. At Kachwekano, the highest mean TRY of 11.7 and 16.6 t ha-1 for inoculum and fungicide treatments, respectively were obtained during season 2010A, and the lowest mean TRY for both spray treatments were recorded in season 2011B. Generally, genotypes at Namulonge
Figure 3.1 a Site x season interaction for area under disease progress Figure 3.1 b Site x season interaction for total storage root yield curve (AUDPC)
Figure 3.1 c Site x season interaction for harvest index Figure 3.1 d Site x season interaction for weevil damage
Figure 3.1 Variation of traits with site and season meaned across genotypes and two spray treatments (inoculated with Alternaria versus sprayed with a fungicide)
Namulonge Kachwekano
60 70 80 90 100 110
2010B 2011A 2011B
AUDPC
Season
Namulonge
Kachwekano
0 5 10 15 20
2010B 2011A 2011B
Yield (t ha-1)
Season
Namulonge
Kachwekano 0
5 10 15 20
2010B 2011A 2011B
Harvest index
Season
Namulonge
Kachwekano 0
1 2 3 4 5
2010B 2011A 2011B
Weevil damage
Season
Table 3.3 Genotype means for Alternaria blight AUDPC values with Alternaria inoculum and fungicide spray treatments at Namulonge and Kachwekano during the 2010B, 2011A and 2011B seasons
Namulonge Kachwekano Namulonge Kachwekano
Genotype 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B
ASP ASP ASP ASP ASP ASP Mean Rank FSP FSP FSP FSP FSP FSP Mean Rank %DR
Araka Red 135.5 114.5 139.0 128.5 142.5 125.0 130.8 24 71.0 60.5 57.0 57.0 67.5 88.5 66.9 22 -48.9
BND145L 121.5 97.0 135.5 107.5 128.5 128.5 119.8 18 57.0 29.0 53.5 46.5 78.0 64.0 54.7 10 -54.3
Bwanjule 114.5 90.0 121.5 97.0 107.5 86.5 102.8 3 53.5 32.5 22.0 36.0 46.5 60.5 41.8 2 -59.3
Dimbuka 146.0 125.0 149.5 128.5 125.0 152.5 137.8 28 78.0 71.0 92.0 60.5 67.5 85.0 75.7 27 -45.1
Ejumula 125.0 107.5 121.5 114.5 107.5 126.5 117.1 15 60.5 50.0 57.0 57.0 50.0 67.5 57.0 11 -51.3
Kigaire 100.5 104.0 114.5 97.0 111.0 104.0 105.2 5 46.5 36.0 32.3 22.0 32.5 60.5 38.3 1 -63.6
Magabali 111.0 97.0 132.0 104.0 118.0 132.0 115.7 11 57.0 46.5 71.0 60.5 64.0 74.5 62.3 18 -46.2
Malagalya 121.5 128.5 125.0 100.5 97.0 111.0 113.9 10 67.5 71.0 50.0 67.5 43.0 53.5 58.8 13 -48.4
MBL 170 97.0 93.5 121.5 118.0 132.0 146.0 118.0 16 29.0 36.0 92.0 57.0 64.0 71.0 58.2 12 -50.7
MBR 536 114.5 79.5 111.0 107.5 118.0 114.5 107.5 6 67.5 29.0 53.5 64.0 50.0 50.0 52.3 8 -51.3
Namusoga 100.5 93.5 132.0 111.0 111.0 111.0 109.8 8 46.5 43.0 53.5 53.5 60.5 67.5 54.1 9 -50.7
New Kawogo 121.5 125.0 135.5 167.0 149.5 174.0 145.4 30 64.0 64.0 113.0 102.5 78.0 78.0 83.3 30 -42.7
NKA103M 100.5 90.0 118.0 139.0 107.5 140.5 115.9 20 36.0 32.5 81.5 78.0 57.0 71.0 59.3 21 -48.8
NKA259L 97.0 100.5 128.5 139.0 114.5 139.0 119.8 4 50.0 39.5 67.5 78.0 57.0 64.0 59.3 5 -50.5
NKA318L 93.5 97.0 135.5 128.5 146.0 146.0 124.4 22 32.5 43.0 95.5 60.5 88.5 67.5 64.6 23 -48.1
NASPOT 1 135.5 149.5 177.5 146.0 170.5 194.5 162.3 8 74.5 85.0 127.0 78.0 106.0 106.0 96.1 7 -40.8
Table 3.3 continued
Namulonge Kachwekano Namulonge Kachwekano
Genotype 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B
ASP ASP ASP ASP ASP ASP Mean Rank FSP FSP FSP FSP FSP FSP Mean Rank %DR
NASPOT 10 O 132.0 107.5 132.0 121.5 132.0 121.5 124.4 26 64.0 43.0 60.5 67.5 74.5 85.0 65.8 27 -47.1
NASPOT 11 107.5 100.5 132.0 93.5 86.5 107.5 104.6 27 50.0 39.5 36.0 39.5 39.5 78.0 47.1 26 -55.0
NASPOT 2 93.5 104.0 128.5 139.0 139.0 160.0 127.3 14 36.0 43.0 99.0 74.5 81.5 74.5 68.1 19 -46.5
NASPOT 3 135.5 90.0 121.5 93.5 111.0 107.5 109.8 29 64.0 39.5 50.0 29.0 60.5 67.5 51.8 29 -52.8
NASPOT 4 121.5 125.0 142.5 132.0 132.0 156.5 134.9 12 64.0 67.5 95.5 81.5 71.0 74.5 75.7 15 -43.9
NASPOT 7 156.5 125.0 146.0 121.5 121.5 148.8 136.6 18 88.5 60.5 74.5 67.5 64.0 88.5 73.9 15 -45.9
NASPOT 8 100.5 111.0 121.5 121.5 118.0 128.2 116.8 20 78.0 53.5 60.5 67.5 64.0 64.0 64.6 19 -44.7
OTADA 114.5 86.5 118.0 123.5 121.5 135.5 116.6 13 46.5 32.5 81.5 60.5 74.5 67.5 60.5 17 -48.1
Semanda 97.0 97.0 121.5 139.0 118.0 142.5 119.2 17 39.5 29.0 81.5 78.0 67.5 57.0 58.8 13 -50.7
Shock 58.5 76.0 97.0 104.0 125.0 111.0 95.3 1 25.5 32.5 50.0 46.5 60.5 43.0 43.0 3 -54.9
Sowola 6 128.5 118.0 128.5 128.5 149.5 133.5 131.1 25 67.5 57.0 81.5 64.0 88.5 71.0 71.6 25 -45.4
SPK004 132.0 114.5 128.5 132.0 111.0 149.5 127.9 23 71.0 60.5 88.5 74.5 57.0 67.5 69.8 24 -45.4
Tanzania 97.0 97.0 107.5 111.0 90.0 86.5 98.2 2 32.5 36.0 25.5 57.0 64.0 50.0 44.2 4 -55.0
Silk Luwero 76.0 104.0 121.5 118.0 111.0 121.5 108.7 7 29.0 32.5 52.7 67.5 53.5 64.0 49.9 6 -54.1
Mean 112.9 104.9 128.2 120.4 121.7 131.4 54.9 46.5 68.5 61.8 64.4 69.4
SE 11.3 9.1 8.4 18.7 14.5 15.0 8.0 5.1 5.1 9.9 21.8 10.5
LSD(0.05) 32.1 25.8 23.7 51.8 41.1 42.5 22.7 14.4 14.6 27.9 61.7 29.7
Seasons 2010B, 2011A, 2011B = the second season of 2010 (September 2010 to January 2011), first season of 2011 (April to August 2011), and second season of 2011 (September 2011 to January 2012), respectively; ASP = inoculated with Alternaria inoculum; FSP = fungicide sprayed; %DR = percentage disease reduction by the fungicide and is the difference between mean AUDPC for fungicide spray and mean AUDPC for Alternaria inoculum spray treatment expressed as a percentage of mean AUDPC for Alternaria inoculum spray treatment
Table 3.4 Genotype means for total storage root yield (t ha-1) with Alternaria inoculum and fungicide spray treatments at Namulonge and Kachwekano during the 2010B, 2011A and 2011B seasons
Namulonge Kachwekano Namulonge Kachwekano
Genotype
2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B
ASP ASP ASP ASP ASP ASP Mean Rank FSP FSP FSP FSP FSP FSP Mean Rank %Yield
gain
Araka red 17.0 14.0 11.9 4.8 8.3 5.9 10.3 11 19.1 15.5 15.3 6.6 10.2 7.7 12.4 20 20.4
BND145L 14.1 21.8 12.2 14.6 7.2 4.5 12.4 4 16.7 27.5 12.0 18.0 9.2 8.1 15.2 5 22.6
Bwanjule 12.2 16.9 9.5 13.3 5.2 3.6 10.1 12 13.5 26.8 12.4 19.3 6.5 4.2 13.8 12 36.6
Dimbuka 4.5 21.8 6.4 11.6 7.9 5.3 9.6 17 8.2 28.0 6.5 16.1 10.6 10.4 13.3 16 38.5
Ejumula 2.4 10.5 8.2 11.7 6.0 3.5 7.0 29 3.2 12.4 10.2 15.4 7.9 4.1 8.9 30 27.1
Kigaire 10.8 18.8 13.0 1.1 3.8 0.8 8.1 23 17.7 21.0 14.0 2.6 4.3 1.6 10.2 26 25.9
Magabali 9.8 8.7 13.6 6.2 5.5 1.7 7.6 26 15.8 17.3 16.3 9.8 8.2 3.2 11.8 22 55.3
Malagalya 4.2 9.3 6.9 10.8 9.7 4.4 7.6 27 5.7 11.3 8.2 14.6 13.8 5.5 9.9 28 30.3
MBL 170 3.8 10.6 10.2 12.8 7.9 6.9 8.7 20 10.1 13.2 11.9 20.2 12.2 8.4 12.7 19 46.0
MBR 536 8.7 10.4 5.4 6.1 5.9 3.6 6.7 30 11.8 20.9 6.8 10.1 9.9 5.4 10.8 23 61.2
Namusoga 9.2 11.5 7.9 10.8 5.1 6.9 8.5 21 14.2 16.5 11.9 20.2 9.2 9.0 13.5 14 58.8
New Kawogo 8.2 6.4 12.0 18.8 10.3 3.2 9.8 6 11.2 9.3 16.8 24.4 12.6 4.3 13.1 17 33.7
NKA103M 11.0 20.7 14.1 9.5 9.0 3.7 11.3 10 13.3 23.1 16.8 14.4 10.1 6.2 14.0 10 23.9
NKA259L 5.4 3.7 4.5 17.0 8.3 7.3 7.7 2 5.8 9.4 6.3 18.9 12.0 6.8 9.9 29 28.6
NKA318L 8.3 5.7 11.2 22.3 12.7 3.1 10.5 18 8.2 11.4 11.7 26.3 10.3 4.4 12.1 21 15.2
NASPOT 1 10.6 12.8 12.6 20.4 8.6 2.9 11.3 15 11.1 22.0 16.7 26.8 11.9 6.4 15.8 4 39.8
Table 3.4 continued
Namulonge Kachwekano Namulonge Kachwekano
Genotype 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B 2010B 2011A 2011B %Yield
gain
ASP ASP ASP ASP ASP ASP Mean Rank FSP FSP FSP FSP FSP FSP Mean Rank
NASPOT 10 O 7.1 18.6 11.0 17.4 5.3 3.6 10.5 22 12.4 28.7 14.0 20.0 8.0 4.3 14.6 6 39.0
NASPOT 11 13.0 14.7 18.7 18.2 13.1 7.5 14.2 3 17.0 23.9 24.4 23.9 17.8 8.0 19.2 2 35.2
NASPOT 2 13.0 13.8 17.0 4.2 6.8 2.9 9.6 1 16.9 24.5 20.5 7.4 9.8 4.2 13.9 11 44.8
NASPOT 3 4.2 18.1 8.8 11.4 10.5 7.0 10.0 16 8.7 21.6 10.8 17.6 12.7 9.6 13.5 15 35.0
NASPOT 4 16.3 7.8 11.8 4.5 3.7 5.2 8.2 5 18.0 14.1 12.9 7.5 5.1 5.5 10.5 25 28.0
NASPOT 7 9.2 18.7 18.6 13.2 6.4 9.9 12.7 25 12.7 25.9 21.6 23.2 9.2 10.4 17.2 3 35.4
NASPOT 8 24.1 23.5 18.2 20.9 8.7 7.3 17.1 9 25.2 30.7 22.7 32.5 11.2 9.5 21.9 1 28.1
OTADA 9.4 7.0 6.1 11.9 5.8 4.8 7.5 28 10.1 12.1 7.2 16.2 8.5 6.5 10.1 27 34.7
Semanda 11.7 23.3 18.8 5.0 3.8 3.7 11.1 7 17.6 26.2 23.0 8.9 5.1 3.7 14.1 8 27.0
Shock 9.3 20.4 8.3 7.8 7.2 7.8 10.1 13 12.2 23.6 8.8 14.3 9.5 9.8 13.1 18 29.7
Sowola 6 3.7 18.8 11.5 11.2 8.5 4.0 9.6 19 5.9 26.5 12.6 15.8 15.7 5.2 13.6 13 41.7
SPK004 4.7 13.7 8.8 12.4 5.7 2.5 8.0 24 6.6 18.1 10.3 16.2 9.9 3.2 10.7 24 33.8
Tanzania 9.3 11.2 10.6 12.6 15.2 4.5 10.6 8 7.7 16.0 13.2 15.4 26.3 6.2 14.1 9 33.0
Silk Luwero 11.3 22.3 10.1 7.7 5.0 4.4 10.1 14 12.3 26.3 13.6 14.4 7.5 11.7 14.3 7 41.6
Mean 9.5 14.5 11.2 11.7 7.2 4.7 12.3 20.1 13.6 16.6 10.5 6.5
SE 2.9 3.6 2.1 3.6 1.5 1.6 3.5 4.6 2.7 4.1 1.7 2.1
LSD(0.05) 8.2** 10.1** 5.9** 10.2** 4.1** 4.6* 9.9** 13.2** 7.5** 11.6** 4.7 5.9
* = significant at P<0.05; ** = significant P<0.01; Seasons 2010B, 2011A; 2011B = the second season of 2010 (September 2010 to January 2011), first season of 2011 (April to August 2011), and second season of 2011 (September 2011 to January 2012), respectively; ASP = Inoculated with Alternaria inoculum; FSP = fungicide sprayed; %Yield gain is the difference between the yield from the Alternaria inoculum spray and the yield from the fungicide treatment for each genotype expressed as a percentage of the yield from the Alternaria inoculum spray treatment
The highest average yield gains of 61.2, 58.8 and 55.3% in response to fungicide treatment were recorded by MBR 536, Namusoga, and Magabali, respectively (Table 3.4). The lowest yield gains of 15.2, 20.4 and 22.6% were recorded by NKA318L, Araka Red and BND145L, respectively. With respect to Alternaria blight severity, treatment with fungicide resulted in variable reductions in severity among genotypes across seasons and sites (Table 3.3).
NASPOT 1 recorded the lowest percentage reduction in disease severity of 40.8% between the Alternaria inoculated and fungicide treated plants. Kigaire recorded the highest percentage disease reduction of 63.6%.
Correlations between Alternaria blight severity and TRY were calculated using the AUDPC values and yield of the Alternaria inoculated plants. Both the AUDPC values and the TRY were meaned over the genotypes and seasons. There were negative but non-significant correlations between Alternaria blight severity and mean TRY across the genotypes during seasons 2010B and 2011A at Namulonge and 2011A and 2011B at Kachwekano (Table 3.5).
3.3.2 Stability of genotypes for Alternaria blight severity, total storage root fresh mass