Effects of intraspecific competition on yield of early potato grown in Mediterranean environment

American Journal of Potato Research, Jul/Aug 2003 by Mauromicale, Giovanni, Signorelli, Paolo, Ierna, Anita, Foti, Salvatore

Accepted for publication 22 May 2003.

ABSTRACT

Since the environment of the Mediterranean regions allows offseason production, potatoes are planted in autumn-winter and harvested in spring. During this period, potatoes are subjected to low temperatures and short day lengths which modify the growth characteristics of plants. For this reason, our analysis of competition response was conducted to better clarify the biological relationship between yield and plant density. Field trials were conducted in Sicily (south Italy), a highly representative area of early potato crop in the Mediterranean Basin, with the aim of studying effects of intraspecific competition on tuber yield and yield components. Ten planting densities (ranging from 3.0 to 8.0 plants m 2) were studied on cv. Spunta using "tuber-pieces" with a different number of eyes (one eye or all the eyes in 1996; one eye, two eyes, or all the eyes in 1997). Intraspecific competition reduced the tuber yield of individual plants, which became gradually less evident with increasing plant density. Competition affected the number of tubers per plant in the lower plant populations only (from 3.0 to 5.8 plants m^sup -2^), whereas effects on average tuber weight were at times more marked in the higher populations (from 5.8 to 8.0 plants m^sup -2^) and at other times in the lower densities (from 3.0 to 5.8 plants m^sup -2^). As a consequence of increased plant density, and notwithstanding the higher intraspecific competition, the yield of tubers per unit area increased linearly. Regardless of the number of eyes per tuber-piece, when passing from the lower to the higher plant density, yield increased from 34.0 to 54.1 t ha^sup -1^ in 1996 and from 39.9 to 56.7 t ha^sup -1^ in 1997.

ADDITIONAL KEY WORDS: Solanum tuberosum, plant density, yield, extra-seasonal cycle.

RESUMEN

Debido a que el clima en las regiones del Mediterraneo permite la produccion fuera de epoca, las papas se siembran entre el otono y el invierno y se cosechan en primavera. Durante este periode, el cultive esta expuesto a temperaturas bajas y dias cortos, lo cual modifica las caracteristicas de desarrollo de las plantas. Por esta razon, nuestro analisis de respuesta a la competencia se hizo para aclarar en mejor forma la relacion biologica que existe entre el rendimiento y la densidad de plantas. Los ensayos de campo se realizaron en Sicilia (sur de Italia), en un area altamente representativa para el cultive de papas precoces en la cuenca del Mediterraneo con el objeto de estudiar les efectos de la competencia intraespecifica sobre el rendimiento y los componentes del rendimiento. Se estudiaron 10 densidades de siembra (que variaron de 3.0 a 8.0 plantas m^sup -2^) del cultivar Spunta, usando "semilla cortada" con diferente numero de ojos (uno o todos los ojos en 1996; un ojo, dos ojos o todos los ojos en 1997). La competencia intraespecifica redujo el numero de tubercules en plantas individuales, lo que se hizo menos evidente con el incremento de la densidad de plantas. La competencia afecto el numero de tubercules por planta solo en las poblaciones bajas (de 3.o a 5.8 plantas m^sup -2^), mientras que los efectos sobre el promedio de peso del tuberculo fue a veces mas marcado en las poblaciones mas altas (de 5.8 a 8.0 plantas m^sup -2^) y otras veces en las densidades bajas (de 3.0 a 5.8 plantas m^sup -2^). Como consecuencia del incremento de la densidad y sin oponerse a la mayor competencia intraespecifica, el rendimiento de tuberculos por unidad de area se incremento linealmente. Prescindiendo del numero de ojos por porcion de semilla, cuando se paso de la baja densidad de plantas a la mas alta, el rendimiento se incremento de 34.0 a 54.1 t ha^sup -1^ en 1996 y de 39.9 a 56.7 t ha^sup -1^ en 1997.

INTRODUCTION

The potato crop in the Mediterranean Basin is usually produced during the winter-spring cycle (from November-December to May-June) and is made possible by choosing locations along the coastal areas that benefit from favorable environmental conditions, namely absence of temperatures lower than 0 C, fertile soils and southern exposure (Foti 1984, 1999; Mauromicale and Ierna 1997). The climatic conditions during this period are characterized by short photoperiod, limited solar radiation and relatively low average temperatures. These conditions have an appreciable effect on plant growth, modifying in a substantial way the morphological and phenological characteristics of crops with respect to those cultivated in the spring-summer cycle. Under winter-spring conditions, for example, most potato cultivars do not flower.

The plant growth characteristics and biological processes consequent to the winter-spring cycle also affect the level of intraspecific competition, which is in turn rendered more complex by the fact that pieces of seed-tuber are often used in place of the whole tuber. In fact, the high cost of seed-tubers leads to their division into pieces of one or more eyes to save the quantity of seed-tubers used per unit area. Consequently, there is a notable variability within the crop because of the different dimensions of the tuber-pieces used, the number of given eyes, and the relative position on the mother tuber, the number of tuber-pieces per unit area, and the number of stems. This in turn varies in relation both to the density as well as the physiological maturity of the seed-tubers, a considerably variable condition in itself, depending on the place of origin of the seed-tubers and conditions during transport and storage. Indicative of this is research carried out by Jannaccone (1957), Foti (1967), Bianco (1975), Longo and Signorelli (1975), and Longo (1977), who have shown significant relationships between plant density, quality of seed-tuber and yield.