Olive Genotypes in Pakistan: Phenology and Pollen Assessment
Pollen viability and germination tests are consider key factors for final productivity. Hence characterization of pollen and phenological aspects of eighteen olive cultivars were studied under an experiment carried out at Barani Agricultural Research Institute, Chakwal, Pakistan. Pollen viability was tested through Acetocarmine and germination was analyzed in the culture media having water, boric acid, sucrose and agar. Results depicted that the maximum number of panicles were recorded in variety Earlik (27.90) and minimum in variety Ottobratica. In general more number of panicles was recorded in 2018 in all most all the varieties as compared to 2017. Highest numbers of flower per branch were observed in variety Ottobratica in both years of study. Staminate flowers were also noted at maximum level again in variety Ottobratica. Maximum final fruit set percentage was recorded in variety Moraiolo (4.23 %) and Coratina (3.70 %) in first year of study while Coratina (3.75 %) and Frantoio (3.59 %) depicted highest fruit set percentage in second year of study. Maximum pollen viability (79.18% & 53.08) was recorded by in Variety Gemlik while minimum values were recorded in Variety Leccino (27.16 % & 47.62 %) in both the years 2017 & 2018 respectively. The germination rate varied among all the varieties. Varieties Ottobratica and Gemlik showed maximum value of pollen germination rate during the study year while minimum rate was recorded again in variety Leccino.
Olive (Olea europaea L.) is an evergreen tree and prominent species of whole Mediterranean countries. Its cultivation can be traced back since ancient times and is also mentioned in the Holy Quran, Hebrew and the Christian Bibles (Flaishman et al., 2008). The olive fruit is a famous fruit tree worldwide for its oil and nutritional benefits. Successful fertilization and fruitlet persistence is directly dependent upon flower quality (Martins et al., 2006) which also predict pistil abortion rate, embrosac development, and receptivity of stigma, pollen viability and nitrogen and carbohydrate contents (Cuevas et al., 1994; Moreno-Aloaas et al., 2018). Large ovaries are associated with more fruit set. (Cuevas and Polito, 2004.) Flower quality is better in off year than on year production (Mazzeo et al., 2014). The length of inflorescence (3-8 cm) and number of inflorescence per branch and number of flower (15-30) per inflorescence varies with the cultivar (Martin and Sibbett, 2005). These characteristic may vary in each year, plant, branch, inflorescence (Brooks, 1948; Cuevas et al., 1994; Lavee et al., 1996; Lavee et al., 2002; Reale et al., 2006). The perfect or staminate flower may vary with the position of inflorescence (Bouranis et al., 1999; Dimassi et al., 1999; Ateyyeh et al., 2000; Cuevas and Polito, 2004).
Most important features in olive fruit set are self-incompatibility, self-fertility and abnormalities in morphological traits. Various factor of sterility are present in olive like more or less related species which are responsible for productivity. Olive trees with good quality and quantity of viable pollens is essential for a good pollination. As a whole, there exists a linear relation between viability and germination capacity of pollen and germination capability in many fruit species (Stanley and Linskens, 1974). Both viability and germination depends on various factors like genotype, nutrition conditions, and biotic and a biotic factors (Khan and Perveen, 2008).Poor pollen viability and germination percentage cause less fecundation in olive (Bini, 1984; Tombesi, 2013). Pollen viability is a genetic trait (Vuletin-Selak et al., 2014) and estimated by various techniques and one of the most important is staining with acetocarmine jelly (Radford et al., 1974).
Pollen germination is another important factor in olive fruit production. Growth of pollen tube in In vitro condition should be check to assess the pollen grain germination capability. Temperature and relative humidity has strong influence on pollen tube growth along with the humidity and growing media.
There is a huge difference in pollen germination on stigma in open field condition and in vitro growth (Heslop-Harrison and Heslop-Harrison, 1981; Pinney and Polito, 1990; Kovacs and Barnabas, 1997). In vitro Pollen tube germination is very sensitive to growing media. In present conditions media is considered to be suitable having water, boric acid, sucrose and agar (Pinney and Polito, 1990) and citric acid (Al-Dehadhehetal et al., 2004).
The media containing 20% sucrose is optimal and more than 30 % cause inhibition of pollen tube growth (Lavee et al., 1985). Pollen ability, germination percentage and pollination of 18 olive cultivars were evaluated. It is believed that pollen ability is an important tool for pollination process for mono orchard cultivation. Major significant differences among cultivars for pollen abilities were listed with variation in characteristic with reference to time (Shemer et al., 2014).
Olive cultivation on commercial scale has no long history in Pakistan. But during the last ten years olive plantation has gained popularity because of its great socio-economic importance. More than 4494.36 hectares have been brought under olive cultivation in Pothwar region and 2,800 acre (280,004 plants) was cultivated other than Pothwar region under Federal and provincial Government, Pakistan (PARC, 2018; BARI, 2019).
A major aim was to examine phenology, pollen viability and germinating capacity of pollens of eighteen exotic olives for identifying the most suitable genotype for newly olive industry establishment.
