Determining Reproductive Parameters, which Contribute to Variation in Yield of Olive Trees from Different Cultivars, Irrigation Regimes, Age and Location

Abstract

Olive (Olea europaea L.) trees can reach a very old age and still bear fruit. Although traditional groves are planted at low density and are rainfed, many newer groves are planted at higher densities and irrigated. As expected, initial yields per area are larger in high density plantations, yet some farmers claim they experience a reduction in productivity with grove age, even in well maintained trees. In order to test the accuracy of this claim and its underlying cause, we measured several productivity parameters in selected branches of trees in seven sites differing in cultivar (‘Barnea’ or ‘Souri’), location and irrigation regime (rainfed or irrigated) for two consecutive years. For each site (cultivar/location/regime), we compared neighboring groves of different ages, altogether 14 groves. There was no consistent reduction in productivity in older groves. Differences in productivity between irrigated cultivars were mostly due to variation in the percentage of inflorescences that formed fruit. Several parameters were higher in irrigated, compared to rainfed ‘Souri’. Differences in productivity between years within the same grove was mostly due to variation in the percentage of nodes forming inflorescences. We studied the expression of OeFT2 encoding a FLOWERING LOCUS T protein involved in olive flower induction in leaves of trees of different ages, including juvenile seedlings. Expression increased during winter in mature trees and correlated with the percentage of inflorescences formed. The leaves of juvenile seedlings expressed higher levels of two genes encoding APETALA2-like proteins, potential inhibitors of OeFT2 expression. The buds of juvenile seedlings expressed higher levels of OeTFL1, encoding a TERMINAL FLOWER 1 protein, a potential inhibitor of OeFT2 function in the meristem. Our results suggest that olives, once past the juvenile phase, can retain a similar level of productivity even in densely planted well maintained groves.

Studying Parameters Affecting Accumulation of Chilling Units Required for Olive Winter Flower Induction

“…The FT protein can travel via the phloem to a nearby meristem and change its fate from vegetative to reproductive [55,58]. In olives, cold temperatures during winter lead to the accumulation of transcripts in leaves-encoding FT proteins, as shown here and previously [10,11]. Abnormally warm natural (shown here) or artificial [10,13] winters inhibit flower induction in olives.…”

“…Olive shoots normally have opposite phyllotaxy, and, as such, the potential number of inflorescences that can develop is twice the number of new nodes formed between spring and fall. In a specific cultivar, at a specific location, the percentage of lateral meristems that will form inflorescences (i) can be highly variable between different years [11]. An olive inflorescence normally contains male and perfect (bisexual) flowers.…”

“…Most bisexual flowers will not develop into fruits. The ratio between the two types of flowers, as well as the average amount of fruit retained on an inflorescence is both genotype and environment dependent [8,9,11]. Olive self-incompatibility [12] is one of the factors contributing to low mean fruit number per inflorescence.…”

“…Thus, the three major developmental factors affecting olive productivity are the number of new buds formed on one-year-old shoots (n), the percentage of lateral meristems that will develop an inflorescence (transition to flowering; i), and the percentage of inflorescences forming and retaining fruit [11]. Here, we focus on factors that affect i.…”

“…Species differ in the environmental and internal signals that trigger the accumulation of FT transcripts in leaves [21]. In olives, the expression of two genes encoding proteins similar to FT increases in leaves during winter and in controlled conditions of 16/10 • C provided in winter or other seasons [10,11]. In trees with high fruit load before winter, the accumulation of FT-encoding transcripts during winter is suppressed [10].…”