1,4-Dimethylnaphthalene Treatment of Seed Potatoes Affects Tuber Size Distribution

American Journal of Potato Research, May/Jun 2005 by Knowles, N Richard, Knowles, Lisa O, Haines, Margo M

ABSTRACT

1,4-DMN is a relatively new sprout inhibitor for use on maincrop and seed potatoes. Despite its registration as a "dormancy enhancer" for seed, relatively little is known about its effects on plant establishment and productivity. The main objective of this study was to evaluate the effects of 1,4-DMN on the productivity of seed potatoes. 'Umatilla Russet' (UR), 'Ranger Russet' (RR), and 'Russet Burbank' (RB) seed tubers were stored at 4, 7, and 9 C over three seasons to create 80-, 554- and 642-degree-day seed, and 1,4-DMN was applied to maintain dormancy several times during each season. 1,4-DMN residue levels at the end of storage were lower in seed aged at higher temperatures. Multiple applications of 1,4-DMN at higher-than-label rates were necessary to effectively inhibit sprouting of seed of all cultivars stored above 4 C. In field trials, depending on cultivar and year, 1,4-DMN either delayed plant emergence slightly or had no effect. 1,4-DMN increased stem numbers from RB and UR seed, but not from RR seed. 1,4-DMN reduced total tuber yields by 3.2 to 5.6 t ha^sup -1^ (5% to 9%), and U.S. No. 1 tuber yields by 4.8 to 7.8 t ha^sup -1^ (8% to 15%) in all cultivars, regardless of seed tuber age. 1,4-DMN also reduced the average tuber weight for all three cultivars and shifted the size distribution from larger (>284 g) to smaller tubers. 1,4-DMN reduced the respective yields of >397-g, 340- to 397-g, and 284- to 340-g tubers by 43%, 19%, and 18% for RR seed, 31%, 14%, and 11% for RB seed, and 40%, 47%, and 27% for UR seed. Conversely, depending on cultivar, yields of smaller tubers (≤170 g) were 11% to 38% higher from 1,4-DMN-treated seed. The shift in tuber size distribution for RR was accompanied by a 1,4-DMN-induced increase in tuber number per plant and per hectare. However, no such effects on tuber set occurred in RB and UR. Moreover, in most cases, the 1,4-DMN effects on yield and tuber size distribution were independent of seed age. Since the 1,4-DMN-induced shifts in tuber size distribution were greater than the reductions in total and U.S. No. 1 yields, 1,4-DMN may be a suitable treatment to reduce average tuber size and increase yield and uniformity of specific size classes of tubers to more closely match market requirements.

RESUMEN

El 1,4-DMN (Dimetil naftaleno) es un inhibidor de brotes de papa relativamente nuevo que se usa tanto para cultivos comerciales como para cultives de semilla. A pesar de su registre como estimulante de dormancia de semilla, se sabe muy poco sobre sus efectos en el establecimiento del plantel y su productividad. El objetivo principal de este estudio fue de evaluar los efectos del 1,4-DMN sobre la productividad de los tubérculos semilla. Tubérculos de 'Umatilla Russet' (UR), 'Ranger Russet' (RR) y 'Russet Burbano' (RB) se almacenaron a 4, 7 y 9 C durante tres campañas agrícolas para producir 80-, 554- y 642-grados-día de semilla y se aplicó 1,4-DMN varias veces durante cada campaña para mantener la dormancia de la semilla. Los niveles de residue del 1,4-DMN al final del període de almacenamiento fueron más bajos en las semillas envejecidas a temperaturas mayores. A temperaturas de almacenamiento por encima de los 4 C se necesitan niveles mayores a los recomendados y aplicaciones múltiplas de 1,4- DMN para inhibir efectivamente el brotamiento de las semillas en todos los cultivares. En pruebas de campo, dependiendo del cultivar y del añe, el 1,4-DMN, retardó ligeramente o no tuvo efecto en la emergencia de la planta, aumentó el número de tallos por semilla de RB y UR, pero no en RR. El 1,4-DMN redujo los rendimientos de 3.2 a 5.6 t/ha^sup -1^ (5 a 9%) en todos los cultivares, sin tener en cuenta la edad del tubérculo semilla. El 1,4-DMN también redujo los rendimientos en el peso promedio del tubérculo en los tres cultivares y cambió la distribución de tamaño de los tubércules grandes (284 g) a tubérculos más pequeños. Redujo los respectivos rendimientos de tubércules > 397 g, 340 - 397 g y tubércules de 284 - 340 g por 43%, 19% y 18% para la semilla de RR, 31%, 14% y 11% para la semilla de RB y 40% 47% y 27% para la semilla UR. Contrariamente, dependiendo del cultivar, los rendimientos de tubércules más pequeños (170 g) fueron de 11 a 38% mayores que en la semilla tratada con 1,4-DMN. El cambio en la distribución de tamaño en RR aumentó el número de tubércules por planta y por hectárea inducida por el 1,4-DMN. Sin embargo, no sucedió lo mismo en RB y UR. Más aún en la mayoría de los casos, los efectos del 1,4-DMN sobre el rendimiento y distribución del tamaño del tubérculo fueron independientes de la edad de la semilla. Desde que los cambio inducidos por el 1,4-DMN en la distribución del tamaño del tubérculo fueron mayores que la reducción en el total de tubérculos US-1, el 1,4-DMN puede ser un tratamiento adecuado para reducir el promedio del tamaño del tubérculo y puede aumentar el rendimiento y la uniformidad en el tamaño específico de las clases de tubérculos para que estén de acuerdo con los requerimientos del mercado.

Accepted for publication 4 October 2004.

ADDITIONAL KEY WORDS: Solanum tuberosum, sprout inhibitor, physiological age, 1,4-DMN

ABBREVIATIONS: 1,4-DMN, 1,4-dimethylnaphthalene; RB, Russet Burbank; RR, Ranger Russet; UR, Umatilla Russet

INTRODUCTION

Methyl-substituted naphthalenes occur naturally in potato tubers (Buttery et al. 1970). Some of these compounds and their structurally related analogs, such as diisopropylnaphthalene, exhibit sprout inhibitory activity (Meigh et al. 1973; Lewis et al. 1997). The volatile compound dimethylnaphthalene (1,4-DMN) is naturally produced by tubers and contributes to the flavor and aroma produced by baked potatoes (Coleman et al. 1981). Beveridge et al. (1981a) examined 20 naturally produced volatile chemicals for sprout suppressant activity and concluded that one of the isomers of dimethylnaphthalene, 1,4-DMN, was as effective as tecnazene (a previously registered sprout inhibitor used on seed in the UK, the registration of which was recently withdrawn). Commercialscale experiments were conducted for both seed and ware potatoes, and 1,4-DMN was found to be effective for sprout control on seed potatoes (at an unspecified storage temperature), but not for ware potatoes stored at 7 to 8 C (Beveridge et al. 1981b).

The EPA registered (Reg. Number 67727-1) a synthetic formulation of 1,4-DMN as a reduced-risk pesticide for use as a growth regulator on stored potatoes in 1995 (Borolo 1995; Bennett 1998). A study published in 1997 found that 1,4-DMN applied as a thermal aerosol fog at 300 mg active ingredient (a.i.) kg^sup -1^ fresh weight was effective as a sprout inhibitor on a short-term basis, but was not as effective as CIPC at 22 mg a.i. kg^sup -1^ fresh weight (Lewis et al. 1997). A more recent study compared the sprout-suppressant activity of 1,4-DMN with CIPC, ethylene and carvone (KaIt et al. 1999). At the end of a 25-wk storage period at 9 C, sprout suppression was greatest with CIPC, followed by carvone, ethylene, 1,4-DMN, and air, in that order. The mode of action of substituted naphthalenes is unknown, but is likely hormonally based (Meigh et al. 1973; Kleinkopf et al. 2003). In contrast, CIPC inhibits cell division, thereby inhibiting sprout growth. Different modes of action no doubt contribute to the relative differences in efficacies of these chemicals as inhibitors of sprout growth. At rates specified on the label, multiple applications of 1,4-DMN are necessary to maintain sprout control during long-term storage (Lewis et al. 1997).

1,4-DMN is currently marketed under the trade names 1,4-seed(TM) and 1,4-Sight(TM), for use as a dormancy enhancer on seed and maincrop potatoes, respectively. In contrast to the relatively permanent sprout-inhibiting properties of CIPC, the temporary sprout-suppressing ability of 1,4-DMN is requisite for the chemical to have any potential use in the seed industry. However, except for early work with different, isomers of dimethylnaphthalene on seed of fresh market European cultivars in Scotland (Beveridge et al. 1981a, 198Ib), little is known about the effects of this chemical on plant establishment and the productive potential of seed tubers. This is surprising in light of the availability of 1,4-DMN to commercial seed growers throughout North America. We therefore initiated a 3-yr study to evaluate the effects of 1,4-DMN on the productivity of seed of long-season russet cultivars important to the fresh market and frozen processing industries in the Pacific Northwest. By manipulating the physiological age of seed tubers during storage, we produced seed with different durations of dormancy and thus sprouting potentials. The effects of seed storage temperature (physiological age) and 1,4-DMN treatments during the storage season on subsequent plant establishment, stem number and tuber yield and grade were evaluated.