|Authors: ||C.S. Pathak, L.L. Black, S.J. Cheng, T.C. Wang, S.S. Ko|
|Keywords: ||Stemphylium vesicarium, Allium cepa, Allium fistulosum, interspecific hybrid, Welsh onion|
Stemphylium leaf blight (SLB) (causal agent Stemphylium vesicarium) is one of the major onion (Allium cepa) diseases of the tropics.
Five Welsh onion (Allium fistulosum) and 106 A. cepa lines were screened in field and laboratory experiments.
All the A. fistulosum lines were resistant or moderately resistant, whereas all the A. cepa lines were susceptible.
Crosses were successfully made between five A. fistulosum and 29 A. cepa lines to introgress SLB resistance into onion lines. 48 crosses thus produced were used for further evaluation.
F1 progenies were evaluated for disease resistance both in the field and laboratory.
All the F1 hybrids were resistant or moderately resistant to SLB. Segregation in the F2 generation was not expected to follow a Mendelian ratio for disease reaction because of high sterility of the F1 hybrids; however, the results indicate possible dominant gene control of the resistance trait.
Moderate pollen fertility (>30%) and low seed set (>5%) was observed in four crosses [CF16 (AC15 X TA198), CF19 (AC50 X TA198), CF19R (TA198 X AC50), and CF52 (AC49 X TA204)]. These crosses were further evaluated for disease resistance and fertility in the F2 and F3 generations.
In the F2 generation there was a marginal increase in fertility among the four crosses.
The crosses CF16 and CF19 had seed set up to 30% in some plants, which were also resistant to SLB. In the F3 generation, resistant plants with high pollen fertility (40-80%) and seed set (20-60%) were obtained in two crosses (CF16 and CF19). In both these crosses A. cepa has was used as a female parent.
CF19 progenies also had fairly well developed bulbs.
The F3 progenies thus generated in this program combine the traits of both the A. cepa and the A. fistulosum parents.
These progenies are now being used in our breeding program to develop SLB resistant onion lines.
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