Tuber Loss Research Articles

Factors aflfecting the development of silver scurf (Helminthosporium solani) on potato tubers

SUMMARYWhen potato tubers with small amounts of silver scurf at lifting (less than 10 per cent of surface cover) were stored over periods of about five months in a dry condition, very little silver scurf developed irrespective of storage temperature. At high humidity, there was little disease after storage at 5°C and very little at temperatures below 4°C: moderate to severe infection (20 per cent or more of surface area covered) occurred at storage temperatures of about 6°C or above. Weight losses of tubers with severe silver scurf (50 per cent surface area affected) stored in a dry atmosphere for 27 weeks were greater than those of tubers with moderate (25 per cent area cover) and slight infection (5 per cent area cover), 8·5, 5·9 and 4·5 per cent respectively. However, tubers stored iti a dry atmosphere showed greater weight losses than tubers stored in a humid atmosphere, despite having less silver scurf infection. Low storage temperatures aggravated symptoms of skin spot.Slightly affected seed tubers gave rise to more silver scurf in the subsequent crop than tubers with over 75 per cent surface affected, and crops from light sandy soils showed more infection at lifting than crops from heavier soils. These differences persisted during storage, but were largely masked if storage conditions favoured disease development, indicating that in normal stocks there is always an adequate inoculum, at lifting to produce severe symptoms. Very small amounts of inoculum giving little silver scurf after storage, resulted from using seed from stem‐cutting material or by treating seed with benomyl.

Bacterial seed tuber decay in irrigated sandy soils of New South Wales

Breakdown of newly sown seed tubers in semi-arid irrigated sands was shown to be caused byErwinia carotovora var.carotovora andE. chrysanthemi. The soil-borne bacterial population appeared to be more important than seed tuber population in initiating rots in soil. Pectolytic activity of tuber-borne bacteria in an anaerobic environment increased with increasing temperature; there was comparatively little rotting below 25°C. Average percentage weight loss of tubers was approximately seven times greater when they were dip-or puncture-inoculated withE. chrysanthemi than withE. carotovora. Control measures should perhaps be based on protection of the newly planted seed tuber rather than on development of clean seed sources. This is the first report ofE. chrysanthemi caused soft-rotting of potato tubers.

Potato Sprout Inhibition by Camptothecin, a Naturally Occurring Plant Growth Regulator1

Abstract An isolate of camptothecin alkaloids was applied to the eyes or sprouts on potatoes (Solanum tuberosum L.) as lanolin suspensions at concentrations of 1.5, 3, 9, and 15 mM, or to the whole tubers as aqueous sprays or dips at various concentrations. Potato sprouting at 15°C was completely inhibited for 4 weeks by all the lanoline suspensions. Inhibition was greater than 95% when a solution of the alkaloids at 5 × 10−1 mM was applied to the tubers as a 3-spray or 3-dip treatment. The camptothecin treatments that inhibited sprouting also reduced weight loss of potato tubers; and even after 4 months at 15°, no symptoms of internal sprouting or other deleterious effects were evident. Electron micrographs of sprouts suggest that camptothecin inhibited sprouting by inducing structural changes in vascular tissues and interfering with cell division in the meristematic portions of the sprouts.

Occurrence, development, and losses associated with silver scurf and black dot on Colorado potatoes

Silver scurf, caused byHelminthosporium solani, and black dot, caused byColletotrichum atramentarium, are pathogens of tuber periderm whose presence in Colorado was only recently reported. A field survey conducted in September 1977 revealed thatC. atramentarium was more prevalent (21.8% tuber infection) and had a wider distribution thanH. solani (5.4% tuber infection). A greater incidence of both pathogens was observed on thin skinned tubers of chipping cultivars (49.0% infection) than on thicker skinned tubers of table stock cultivars (9.1% infection). Conidial development ofH. solani is tretic, pleurogenous, and requires 17–21 hours per conidium. Conidial septations appear while conidial elongate, and require 3–5 hours per septum. Light microscopy revealed that at least 11 conidia per conidiophore are produced in culture in 54 hours at 20–25 C (68–77 F) and humidity >90%. Scanning electron microscopy showed that fructifications ofH. solani (conidiophores-conidia) arise from beneath infected tuber periderm. Histological studies indicate some peridermal loosening and sloughing. Heavy deposition of unidentified compounds was observed in infected periderm, and hyphae were restricted to periderm cells. Fresh weight loss of tubers naturally infected withC. atramentarium was significantly greater than fresh weight loss of nearly noninfected (< 1% surface area infected) control tubers. Periderm infected with eitherH. solani orC. atramentarium appeared similar, i.e. shriveled, suggesting infections from either pathogen may result in increased fresh weight loss through alteration of the periderm.

A re-evaluation of the Dionne method of vegetatively doubling the chromosome number in potato

The efficiency of a published method (Dionne) of vegetatively doubling diploid potato clones by treating the nodal sub-axillary meristems of grafts with colchicine was investigated. Calculations of shoots per graft, tubers per shoot, tuber losses, and doubling frequencies in the three germ layers (LI, LII and LIII) of plants grown from tubers, indicated that one might expect 0.5 completely doubled plants per graft. Clone/shoot regeneration interactions etc. will greatly affect the efficiency in specific cases.

Thermotherapy of potato leafroll

Heat treatment at 35 C for 56 days or at 36 C for 39 days completely eliminated leafroll virus from tubers of several potato varieties. Tuber size had little effect on ability to survive the treatment or on the time required for the elimination of leafroll. Tuber losses after heat treatment range from slight to as high as 50%. Heat treatment materially delayed development of sprouts and consequent plant emergence. It appeared to have little effect on either virus X or spindle-tuber virus. An equation and graph are presented to show the relationship of time and temperature to the elimination of leafroll virus in these experiments and some conducted by others. Heat treatment has proven of value in the elimination of leafroll virus from small lots of seed of special value in a breeding program.

Fumigation of agricultural products. II.—Susceptibility of seed potatoes to the vapour of methyl bromide

AbstractThe susceptibility of potato tubers to methyl bromide vapour has been measured by two criteria of damage: the loss of tubers rejected before setting and the reduction of yield per viable tuber. Varietal differences are more clearly shown by the latter criterion, as expected, and less clearly by the former. The damage caused by raising the dosage above a critical level has on the contrary much less influence on the yield per viable tuber than on the loss by rotting in storage. This critical level fluctuates widely, probably seasonally. Tubers fumigated in the autumn are enabled to reverse much of the phytotoxic action of the fumigant and losses are much less severe than if the fumigation takes place in the spring immediately before planting.