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PETERS: DISEASES IN PEAT SOILS IO 5

Jones, It. A., and Borthwick, H. A. 1938. Influeuce of photoperiod and other factors on the formation of flower primordia in the potato. Amer. Potato Jour. 15:331-336.

Stevenson, F. J., and Clark, C. F. I933. Artificial light as an aid in potato breeding. Amer. Potato Jour. lO:1O3-1o7.

Werner, H . O . 1934. The effect of controlled nitrogen supply with differ- ent temperatures and photoperiods upon the development of the potato plant. Nebr. Agr. Exp. Sta. Res. Bul. 75.

1941. Flower and berry production by potatoes as influenced by two light intensities and two midwinter planting dates. Amer. Pota- to Jour. 18:349-355.

S U R V E Y O F P O T A T O D I S E A S E S I N P E A T S O I L S I N C A L I F O R N I A

E. J. PETERS

Research Department, Weyl-Zuckernaan & Co., Stockton, Cal.

T'he wi l t ing of pota to vines in commercia l fields is one of the first indicat ions that the p lant is not normal . A l though it is of common occurrence it is impor t an t to ascer ta in the real cause of it. The cor- rect d iagnosis very often leads to measures that will reduce or el iminate the t roubles in the future. Hi'owever a p rope r diagnosis of the wi l t ing condi t ion of plants g rown in peat soils does not appear to be a s imple

mat te r for field n-~en.

O u r observat ions were made in the morn ing in o rde r to exclude all types of day wil t ing. Thousands of p lants were pul led and the dis- ease could be readi ly de te rmined in the field. T o de te rmine the prob- able cause of wi l t ing in near ly 2ooo acres of pota toes g rown in the peat soils of California, l abora to ry examina t ions were made of all p lants picked up in the field since wi l t ing is somet imes associated wi th lesions on the g round line.

T h e s t anda rd med ia for isolat ion of fungi and bacter ia were used th roughou t all invest igat ions. The pa thogenic i ty of the isolated organ- isms was p roved by mak ing inoculat ions into po ta to tubers .

Of the I2 9 p lants carefully cul tured in the l abora to ry the fol lowing organ isms were r ecove red :

The author wishes to express his gratitude to Drs. M. W. Gardner and P. A. Ark of the Division of Plant Pathology of the University of California, for their kindness in permitting the use of laboratory facilities, which have made thi~ investigation possible.

io5 T H E AMERICAN POTATO JOURNAL [Vol . 19,

88 plants Rhizoctonia solani . . . . . . . . . . . . . . . 68.2 pe r cent 2 7 " Black leg Erwinia phytophthora.. 20. 9 . . . .

6 " Black leg and Rhizoctonia solani.. 4.7 . . . . 4 " Black leg and R ing Rot Phyto-

monas sepedonica . . . . . . . . . . 3. I . . . . 4 " R ing Rot Phytomonas sepedonica. 3.1 . . . .

I t mus t be emphasized that in most cases (68.2 per cent) where the ex te rna l appearance of the vine resembled a typical case of the black leg disease Erwinia phytophthora, Rhizoctonia solani was isolated in pure culture. A cr i ter ion used for d iagnos ing the disease as black leg was the descr ipt ion of the disease by Appe l and Leach and the opinion of pract ical farmers . T h e black leg organism, Erwinia phytophthora in pure cul ture was isolated in 20. 9 per cent of the cases whereas in 7.8 per cent of the cases it was associa ted with o ther pathogenes.

This survey of wi l ted p lants g rown under the condi t ions ob ta in- able in pea t soils, poin t to the need of a more careful and a more cr i t - ical examina t ion of p lants in the field and, if {acilities permit , l abora to ry tests mus t be pe r fo rmed to ascer ta in the causal agent .

L ITERATURE CITED

Appel, O. 19o2. Der Erreger der "Schwarzbeinigkeit" bei den Kartoffeln. Berd. d. deut. bot. Ges. 2o; 32-35.

- - 19o 3. Untersuchungen fiber die Schwarzbeinigkeit und die durch Bak- terien hervorkerufene Knollenfiiule der Kartoffel. K. biol. Anst. f. Land. -u. Porstwirt. Arb. 3: 364-432.

Leach, J. G. I93I. The black leg disease of potato in Minnesota. iVfinn. Agr. Exp. Sta. Tech. Bull. 76.