P R O P A G A T I O N O F P O T A T O BY S T E M C U T T I N G S 1

E. F. COLE AND N. S. WRIGI-IT 2

I NTRODUCTIO N

With the development of techniques to select potato tubers which are free of mild strains of potato leaf roll virus (3) and from which potato virus X has been eradicated (2) there arose a need to achieve rapid and extensive increase of desirable sub-clones. Tests were made to determine if stem cuttings rooted in the greenhouse and then transferred to the field would grow well and produce tubers. This paper gives the results of these tests.

~V~ATERIALS AND ~/[ETItODS

Propagation tests were made with the varieties Kennebec, Netted Gem, Norland and Saco. Plants were grown in 8- or 10-inch clay pots in the greenhouse from seed pieces or eyes which were planted at various times during the winter and early spring. When the plants were 10 to 12 inches tall, the tips were removed to stimulate axillary growth of stems. When these reached about 5 inches in length their tips, ap- proximately 2 inches long, were removed and set in washed, sharp sand with the cut surface down. The flats or pots containing the sand were placed under intermittent mist in the greenhouse to ensure that the cuttings were kept moist. About 2 weeks later the cuttings on which a good root system had developed were transplanted to soil in the greenhouse or, if it was time for field planting, were prepared for shipment to field sites.

The plants retained in the greenhouse were used to produce more cuttings. Those to be shipped to field sites were either removed from the sand, wrapped in plastic, and shipped by mail, or they were transported by road while still in the sand. With the latter method the cuttings, if watered, may be held for 10 days or so before being planted. Field planting was done in late May. Plants were set in the bottom of a 6-inch-deep furrow but only the roots were covered at the time of planting. As the plants grew more soil was added to the furrow and eventually some hilling was done. Tubers were harvested after the plants died.

RESULTS

Potato stem cuttings made any time during the winter or spring rooted in moist sand in about 2 weeks under normal greenhouse con- ditions. The four varieties rooted equally well without hormone treatment. A typical rooted cutting is shown in Fig. I. Rooted cuttings planted in soil in the greenhouse produced vigorous growth from which more cuttings were taken. Cuttings packed in moist vermiculite in plastic (Fig. 2) withstood 3 days in the mail without loss but became somewhat chlorotic due to lack of light. However, those hauled to the field while still in the sand in which rooting occurred (Fig. 3) were in ideal condition

IContribution No. I]9 from Research Station, Canada Department of Agriculture, 6660 N.W. Marine Drive, Vancouver 8, B.C. Canada. Accepted for publication Jan- uary 19, 1967.

2Plant Protection Officer and Plant Pathologist, respectively.

301

302 AMERICAN POTATO JOURNAL [Vol . 44

FIG. 1.--Cutting ready /or packaging, shipping, and planting. The root system is well developed. The cutting had been in sand in a mist chamber for 14 days.

FIG. 2.--One method of packaging cuttings for mailing. Moist vermiculite in a plastic bag holds 18 cuttings. The bag is closed with an elastic band, wrapped in cardboard

and packed in a carton.

FIG. 3.--Sixty cuttings of var. Kennebec in a 13xl8-inch greenhouse flat, 14 days after being set in sand.

1967] COLE AND WRIGHT: PROPAGATIONt BY STEM CUTTINGS 303

FIG. 4.--Nine plants of var. Kennebec, 30 days after planting the cuttings.

Fie. 5 .--Tuber yield of five plants grown from cuttings and five "control" plants grown from tuber seed pieces.

for planting. Rooted cuttings produced vigorous and uniform plants (Fig. 4) and a good yield (Fig. 5) although some tubers were somewhat rough. Plants produced from cuttings matured at least 2 weeks earlier than those produced from tubers.

DISCUSSION

The number of plants obtainable by stem cuttings all derived from a single tuber is substantially more than the number produced by sprout

304 AMERICAN POTATO JOURNAL [Vol. 44

excision (1) . In fact, the number produced is determined, within prac- tical limits, mainly by available greenhouse space. Eight plants produced from a single tuber in December will yield at least 5000 rooted cuttings by early May. A 13- by 18-inch greenhouse flat will accommodate 60 cuttings.

Occasionally, rooted cuttings will produce a single tuber on the callus while it is still in the rooting medium. Only if such a tuber is removed will stolons and normal tubers form later. In the field care must be taken to ensure adequate moisture for the transplants. Since stolons and tubers originate from the lower axils of the cuttings it is important to add more soil to the trench as required. The roots of a fully grown plant should be 6 to 8 inches below the surface of the soil.

SUMMARY

Stem cuttings of potato placed in moist sand in the greenhouse developed roots within 2 weeks. The rooted cuttings when transplanted to the field became vigorous and high yielding plants. Stem cuttings were used to obtain rapid and extensive increase of desirable sub-clones.

RESUMEN

Las cortaduras del tronco de la papa colocadas en arena humeda en el invernadero hacen raices en 2 semanas.

Las cortaduras arraigadas al transplantarlas en el campo hacen plantas vigorosas y de grande producci6n. Cortaduras del tronco fueran usadas para obtener aumento r~pido y extenso de los sub-clones deseados.

ACKNOWLEDGMENT

The writers gratefully acknowledge the assistance of Mr. Fred Groess- her, Greenhouseman.

LITERATURE CITED

1. Buck, R. W. Jr. and R. V. Akeley. 1966. How to obtain the most plants from one potato tuber. Amer. Potato J. 43: 128-130.

2. Mellor, F. C. and R. StaLe-Smith. 1967. Eradication of potato virus X by thermotherapy. Phytopathology 57 : 674-678.

3. Wright, N. S., H. R. MacCarthy and E. F. Cole. 1967. Detection and control of mild strains of potato leaf roll virus. Amer. Potato J. 44: 245-248.