VII.
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
Based upon the results of our extensive surveys we conclude that potao
blackleg and soft rot is one of the major diseases of potato crop in Khyber
Pakhtunkhwa. Moreover, E. carotovora subsp. carotovora (Ecc) is as much important
as Erwinia carotovora subsp. atroseptica (Eca) in causing the disease in potato crop
whereas E. chrysanthemi (Ech) is a minor pathogen. As regard the overwintering
places of the pathogen, infected tubers are the best source of primary inoculum
followed by diseased plant debris. In terms of genetic diversity, Eca isolates are
genetically different from each other by as much as 40%, these differences are not
tightly correlated to the pathogenic differences found among them. As blackleg and
soft rot of potato is a hard-to-control disease, an integrated disease management
(IDM) is the best strategy. Among aqueous plant extracts, as a component of the
IDM, neem extracts are one of the best. A fertilizer combination of N3P1K3
(262/252/262 kg.ha-1) which is slightly higher than the normally practiced dose
(247/247/247 kg.ha-1) is helpful in bringing the disease to a minimum and
subsequently increasing the yield. Among different potato varieties available to our
local farmers, field performance of variety Kuroda is comparatively better whereas
variety Desiree is the most susceptible.
We tried to explore a lot of areas about the diagnosis, and molecular diversity
of the pathogen and management of the disease it causes. However, there are still
many un-answered questions. For example, the patterns generated from RAPD
analysis of our studies demonstrated considerable variability among Eca isolates of
the North-Western Pakistan. But our study used only 20 Eca isolates. The study could
be extended to include as many as 200 Eca isolates. The knowledge of diversity
among a large group of Eca isolates would give us a better and clearer picture of the
genetic variation found in this pathogen. Likewise, finding of unique RAPD (if it is
discovered) band might enable us to clone, sequence this band and use it for designing
unique primers (to be used in the detection and identification of the pathogen).
Similarly, our plant extracts seem to be contact-dependent i.e., they kill bacteria on
direct contact. If bacteria are just below the skin of the tuber, deep inside the tuber or
bulb or present inside plant tissue, can these extracts penetrate through lenticels/other
natural openings and kill them? Further research is needed to answer this question.
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Determination of the cost-benefit ratio as well as the precise identification of the
active anti-microbial metabolites found in these plants need to be investigated.
Research on the purification, characterization, formulation, activity period (time
interval during which these anti-microbial metabolites are effective after their
application as seed treatment, sprays or soil drenches) and effective dosage of these
plant metabolites is also needed.
Recommendations
As infected tubers are the best source of primary inoculum, it is recommended
that disease-free tubers should be used as source of seed. Alternatively, seed tubers
should be treated with aquous plant extracts such as neem extracts to kill the tubersurface-borne inoculum. The finding that Eca isolates could genetically differ from
each other by as much as 40% suggests that the pathogen is heterogeneous and could
pose threat to breaking the resistance of resistant potato varieties. Therefore, it is
recommended to have as many moderately resistant varieties as possible. On the
control side, an integrated disease management (IDM) strategy is recommended. As a
part of IDM, a fertilizer combination (NPK, 262/252/262 kg.ha-1) which is slightly
higher than the normally practiced dose (NPK, 247/247/247 kg.ha-1) should be used.
If acceptable to local farmers, the relatively less susceptible potato variety Kuroda
(longer duration) should be used rather than the more susceptible shorter duration
variety “Desiree”.
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