TOMATO-FRUIT DISEASES.

New Zealand Journal of Agriculture, Volume XII, Issue 3, 20 March 1916, Page 198

TOMATO-FRUIT DISEASES.

CURRENT INVESTIGATIONS.

R. WATERS,

Biological Assistant.

Tomato-fruit in the vicinity of Carterton, Wairarapa, has been affected this season by several diseases, one of which appears to have been not recorded so far in New Zealand. As this disease was suspected of causing diarrhoea and similar illness to the consumers of affected fruit, a rapid ' investigation was undertaken, and the following notes are presented for the. information of growers generally. The crops dealt with were growing out-of-doors. The root, stem, and leaves of the tomato - plants] examined were practically free from disease. On the fruit, however, three -apparently separate affections were namely, (i) Tomato blackrot. (Macros'porium- tomato), t (2) circular white patch, . and .. (3) premature softening.

tomato black-rot {Macrosporium tomato).

Attention has previously been drawn in the publications of the Department to this very destructive disease, which . doubtless is now well known to many growers. The disease on the present occasion was found prevalent particularly amongst the. more wrinkled varieties, which often seemed to expose internal tissues through unequal growth tearing the flesh about the blossom , end. Dark spots appear, especially toward this end, and these spots enlarge until more than ,half the fruit . may be flat or sunken (Figs, i and 2). On such injured surfaces black or greenish-black velvety

mould occurs, bearing enormous numbers of minute olive-green spores (Fig. 3). By the latter appearance the disease may be detected. • ’ ~ ‘ I. . Though formerly ' tomato black-rot was regarded as distinct from potato leaf-curl (Macrosporium solani), more recent observers are inclined to believe that the two are ’ identical; growers would

therefore be well advised at least to treat . them as such. When the fungus is established upon a ripening crop, as in this case, the collection and the destruction by burning or by burying deeply

all affected fruit is the best treatment that can be advised. Simultaneous Bordeaux spraying limits the infection of unaffected fruit. As soon as the ■ crops are harvested it is necessary to destroy similarly all diseased tomato or potato material. The following season the crop should advisedly be grown on land not previously occupied for some years by either tomatoes or potatoes. Damp or

badly drained land and badly ventilated glasshouses encourage black-rot, and it spreads rapidly in plants only partly supported or altogether growing over the ground. Fresh stable manure should not be used. Early and thereafter regular mixture ' next season would do • much ' of an attack.

applications of Bordeaux to prevent a recurrence

CIRCULAR WHITE PATCH.

Treating of this affection, there were observed to be common on the upper surfaces of the fruit directly exposed to the midday sun large patches, first appearing as light-yellowish areas in the skin and the firmer thick fleshy tissue just , beneath, which latter together form the casing holding the pulp and give the shape to the fruit. Outside of these areas the fruit was reddening as usual. Later the tissues of the bleached patches collapsed into sunken, flat, somewhat circular, finely wrinkled white patches,, sometimes over an inch in diameter. The firm, tissue under the skin by this time had dried,' adhering closely’ to the under-side of the skin, with which it then formed a thin casing expanding to normal

thickness only at the periphery of the circle. Under these patches the pulp . surrounding the seeds was moist and sometimes milky white. This was seen under the microscope to be due to the accumulation in the pulp-cells of enormous numbers of starch granules, which also were abundant in the cells of the dried skin and adjacent tissue. \ ' The general appearance of ' this affection ■is so distinctive that it should readily be correlated with any- previous description had it been recorded. So far, however, I have been unable to find any mention of such injury, nor could any traces of a causative fungus be found. The conversion of soluble reserve food into starch, which accumulates in granules, takes place under ordinary

circumstances as the fruit develops. These granules are later reduced to a sugar or similar soluble form, in which some of it may then, pass on to the seeds or' other growing parts requiring nourishment. The assemblage of granules in such enormous numbers as in the cases noted, however, is quite extraordinary, and somewhat discounts the likelihood of the trouble being due to an organism which was drawing upon and reducing the reserve material. I am inclined to regard the disease as a physiological one brought on by some unfavourable weather-conditions, of which the heat of the sun acting upon the previously damaged portions. caused the final dried and bleached appearance. Nevertheless specimens will be kept under observation. Should, any grower have had experience with this trouble the Biology Section of the Department would be glad to co-operate with him in arriving at its origin. PREMATURE SOFTENING. This trouble seems indistinguishable from the ordinary softening of overripe fruit, and but for its occurrence upon specimens just turning colour one would have thought it was nothing but the natural ripening process.. Affected fruit appeal' to soften in patches that exhibit an almost imperceptible change in colour and ■in the transparency of the skin. To this condition were attributed certain qualities in the fruit injurious to the consumers. . This, in fact, was the only aspect of the matter immediately important to the grower in the present instance, who was withholding the sale practically of his entire cropvalued at £2ooon account of several cases of illness reported to be due to his fruit. Experiments with typically affected fruit indicated that there was little fear of such disorders arising from the tomatoes as he marketed them. He was consequently advised by telegram to proceed at once with the sale of the fruit. The softening in patches of ripening fruit may be merely the incipient stages of the white-patch condition, which was found much more abundant throughout the crop. Further observations in this direction will be made.

Cultivation given to the lucerne at Ruakura during the latter part of January had a wonderful effect on the succeeding crop. Rye-grass, Yorkshire fog, catsear, and sorrel, which had constituted the principal weeds in the lucerne, were almost absent from this growth. The cultivating operation was carried out under ideal weather-conditions, a hot sun rapidly withering up the weeds after they had been dragged out by the cultivator and harrows.