CERTIFIED POTATO SEED

Sun (Auckland), Volume IV, Issue 1034, 26 July 1930, Page 27

CERTIFIED POTATO SEED

Grading Standards For Current Season’s Crop Though the demand for certified seed potatoes is increasing very rapidly, it is evident that the merchant and the Department of Agriculture have different conceptions as to what should constitute the main features of certified seed. The merchant demands varietal purity and careftil grading, so that the seed may be of good appearance and readily saleable. The department is concerned also with varietal purity, but takes into account more particularly what is termed the “cropping power,” and it has left the question of grading for arrangement between the vendor and the purchaser. The department aims at the distribution of seeds capable of giving satisfactory yields, and this factor is not one that can be judged from the superficial appearance of the tubers.

It is, however, evident that both points of view require consideration, and the present object is to explain the difficulties encountered in attempting to set definite grading standards, and what steps are being taken to remedy the somewhat unsatisfactory position existing at the present time, writes Mr J. W. Hadiield, Agronomist to the Department of Agriculture in the April “Agricultural Journal.” Tags used in connection with certification have printed thereon a statement to the effect that grading is a matter left entirely between vendor and purchaser. Nevertheless, in the 1928-29 season a method was introduced by which the certifying officer could indicate on the tag, by the use of certain figures, the grading of the seed within that sack. No attempt was made to define standards for certified seed, but merely to indicate the grading of the line under inspection, so that tlie vendor could quote these grading figures when offering his seed; or, on tlie other hand, the purchaser could, in a very simple manner, stipulate a certain definite grade. Generally speaking, growers understand the significance of these figures, but as a rule the merchants have either disregarded them or not understood their import, and an attempt is made here to explain in detail the scheme as intended it should apply to the produce of the 1929-30 season. It seems necessary to explain, in the first place, why definite standards have not been fixed for certified seed. Such a proposal met with strong opposition from merchants in Canterbury who were handling most of the certified seed. They are called upon to fill orders from all over the Dominion, and the requirements of-one merchant or one district may be very different from that ofc unother in regard to the size of seed. Some purchasers require “table” size for cutting and planting, and, since this practice is one that the department strongly recommends, it would be a retrograde step to refuse to certify to tubers of this size. There can be no one standard to fill all requirements, and therefore it must fall to the purchaser to stipulate the grading standard, and the method here described facilitates this to a very large degree. Uniformity in Size Necessary. One requirement is probably universal—that the tubers should be reasonably uniform in size, irrespective of whether the demand is for large, medium, or small seed. A grading standard should therefore Convey in simple terms (1) the average size of the tubers, and (2) the range in size—that is, uniformity of grading. The average weight of tubers may be 3oz in a line ranging from loz to Boz, but will not be as well graded as a line having the same average weight but ranging in size from 2oz to 4oz. The use of sieves to determine size Is unreliable, giving varying results according to the way they arc used and the tuber-shape of the variety. Moreover, growers would have Vo purchase a whole range of sieves. On the other hand, probably every home has a set of moderately reliable scales, and hilling tuber-weights Is both accurate and coilreniest, and falls into line with th*

custom of referring to the size of tub-sr; in terms of ounces. It has already been explainer) t/xa? the average weight gives no iudi-*iioi of the uniformity of grading, nut th< degree of uniformity may he indicated by taking at random a definite numbei of tubers from each sack till 100 art obtained. If these are laid out on the ground they represent 10 the eye the average grading of-the sacks sampled To convey this grading in terms ol figures the method adopted is to separate by eye measurement the 10 largesi and the 16 smallest tubers. If these lots are weighed separately the weight will convey, after some little practice, a rea•sonablv. accurate idea of the standard of grading in that particular line. Sixteen tubers afford a convenient number, because if the weights are recorded in pounds they indicate also the average weight a tuber in ounces. Thus a line grading “6/3” means that the 16 largest tubers weigh 61b as against 31b for the 10 smallest. It also indicates that the average weight of the 16 largest tubers is 6oz, and the average of tho 16 smallest 3oz. The range is from round übo«. Ooz to round about 3oz. A few tube*, will be over 6oz and a few below 801 These grading figures are always to & found on the tags attached to the saclUv by the grower. If the merchant »v grades, the figures, of course, fail be of any value. . The. final tuber-inspection for certinotion is undertaken when the seed i? graded, in sacks, ready for sale. At least one sack in every six is opened up (with a minimum of eight sacks in an\ one line) and 25 tubers are taken at random from every sack opened. Eacli lot of 100 tubers is weighed for the grading standard. Each tuber is inspected, and a certain proportion cut to determine the percentage of disease present. Grading the 1929-30 Crop. In regard to grading, the following standards will be adopted for the 192930 seed crop : (1) If the 16 largest tubers weigh under 21b the line should be rejected. (2) If the 16 smallest tubers weigh under If lb the line should be rejected, but may be regraded and again inspected at the convenience of the certifying officer. (3) If tlie 16 smallest tubers weigh more than 4-Jlb the grading figures should be indicated on the tag and the tag branded “tabic.” (4) If the difference between the weight of the 16 smallest tubers and the weight of the 16 largest tubers exceeds 2Alb the / line should be rejected for inefficient grading, but may be regraded and inspected at the "convenience of the certifying officer. Purity and Disease Standard. In this connection the certifying officer will reject if there are present more than 2 per cent, of rogues (foreign varieties), 3 per cent, of iate blight, 4 pei cent, of powdery scab, 2 per cent, oi bacterial rot, 4 per cent, of potato moth. 4 per cent, of eel-worm, >r 7 per cent of dry-rot, badly scabbed, or badly dam aged tubers. Ihese standards are not permanent They represent a tightening of the previous season’s regulations, and it is probable that the following season will see the percentages of rogues and dis ease allowed in certified seed still fur tlier restricted.