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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 “tuberpieces” 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−2), whereas effects on average tuber weight were at times more marked in the higher populations (from 5.8 to 8.0 plants m−2) and at other times in the lower densities (from 3.0 to 5.8 plants m−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 54.11 ha−1in 1996 and from 39.9 to 56.7 t ha−1in 1997.

Shifting harvest period from spring to autumn-winter-spring of seed-grown globe artichoke varieties, by a correct combination between sowing date and gibberellic acid-(GA$_3$ ) applications, may have effects on the suitability of heads (capitules) for the market. A two-year-study was carried out in Sicily (Southern Italy) to check the effects of harvest period (from November to April), sowing date (from 1 July to 20 August) and GA$_3$ (0, 1, 2 or 3) applications per plant on characteristics of heads of ``Orlando", a new F$_1$ seed-grown hybrid of globe artichoke [Cynara cardunculus L. var. scolymus (L.) Fiori]. Anticipating the harvest time from April to November, early sowing or 2 or 3 consecutive GA$_3$ applications, generally decreased the head weight, increased the head length/width ratio, and the stalk length. These effects did not affect the market suitability of ``Orlando" heads. They were less evident on heads of ``Violetto di Sicilia", a traditional vegetatively propagated variety that usually produces heads from November to April.