1. M.G.TEKLU, T.H. BEEN, C.H. SCHOMAKER & J.E. BENIERS
The effect of temperature and time on the population dynamics of M. chitwoodi in potato tubers during storage.
M.G.TEKLU, T.H. BEEN, C.H. SCHOMAKER & J.E. BENIERS
Introduction
Results
Storage conditions of potato tubers for seed, ware, or industrial processing vary in storage time and temperature. Several processes (can) occur: respiration, sweetening, but also rotting, sprouting or possible multiplication of pathogens within the tuber. One of the latter is M. chitwoodi, a quarantine pest, which might increase in numbers when infested tubers are stored.
Objectives
To study the population dynamics of M. chitwoodi in tubers with varying storage temperature and time.
To assess possible viability of infective juveniles after different storage temperature and time.
Fig 3. Exponential model showing the population dynamics of M. chitwoodi with storage time at three temperatures.
Materials and Methods
Tubers of the susceptible cv. Désirée were produced at a Pi of 12 J2 g-1 dry soil and sorted into classes based on their tuber-knot index.
Tuber lots were stored at 98% RH, at 4, 8 and 12oC and nematode numbers were assessed after 0, 2, 4, 6 and 8 months of storage.
Before processing tuber lots were acclimatized for 2 weeks at 18-20oC to harden their skin.
Tubers were then peeled and nematodes were extracted from the peel using a Seinhorst spray mist-chamber.
For each combination of time and temperature a minimum of 12 replications were used to extract the nematodes from the peel.
Nematodes in 50 g of peel, after 6 and 8 months of storage time (different Pi’s), were tested for viability by reproducing them on the cv. Désirée in a pot test. Pf was estimated from roots and tubers.
Fig 4. Population dynamics of J2 of M. chitwoodi, originating from tubers stored for 6 and 8 months at 4, 8 and 12 oC, in a pot test on the susceptible cultivar Désirée (roots only).
Discussion A B
Reduction of population densities at 4 and 8oC might be associated with increased sugar levels (sweetening) of stored potatoes.
Juveniles, surviving 6 and 8 month of storage, proved to be viable and were able to multiply on roots and tubers.
Re-calculated final population densities of J2 recovered from roots only, amounted to a minimum value of the maximum population density M, of 50 J2 per g of dry soil.
Contrary to numerous quotes in the literature, nematodes in the infected tubers, even at 12oC, did not multiply.
Fig 1. M. chitwoodi infected tubers were sorted based on their TKI values (A: class II, B: class IV).
Conclusions
Both storage temperature and time influenced the population densities of M. chitwoodi in the potato tubers.
Reduced population densities of M. chitwoodi at 4 and 8oC could not guarantee for clean tubers as the surviving juveniles of these tubers were still able to reproduce.
A follow up is needed to investigate tuber infection levels of stored partially resistant potatoes in time at different temperatures.
Acknowledgement: NVWA of The Netherlands (Loes den Nijs) for their valuable financial support .
Fig 2. Tuber peel of 0.5 cm deep and cut in to pieces of 1 cm2 (left) and 30 g of sub-sample of peel placed in the mist-chamber for 7 weeks to extract nematodes from each storage time and temperature (right).
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