Advances in Plant Breeding Strategies: Fruits by Jameel M. Al-Khayri & Shri Mohan Jain & Dennis V. Johnson

Author:Jameel M. Al-Khayri & Shri Mohan Jain & Dennis V. Johnson
Language: eng
Format: epub
ISBN: 9783319919447
Publisher: Springer International Publishing

13.5 Environmental Components: Flowering, Breeding Behavior and Fruit Setting

Among different environmental components, temperature , photoperiod and water play major roles in regulating timing and intensity of flowering in mandarins. Hence, frequency of flowering varies in different regions having variable climatic conditions. The climatic factors also effect flower types, distribution on the tree, fruit set percentage and yield .

13.5.1 Floral Bud Induction and Differentiation

In citrus , vegetative growth stops in the winter season (rest period) in sub-tropical and dry tropical regions. Shoot growth ceases and root growth decreases when temperature falls below 12 °C and flower bud induction begins (Davenport 1990; Krajewski and Rabe 1995). In Satsuma , flower bud differentiation was observed in late December in Japan (Iwasaki et al. 1959). However, in early November, treatment of trees at a high temperature of 25 °C along with defoliation, initiated flower bud development before morphological differentiation (Nishikawa et al. 2007). Floral induction and bud development require different temperatures and seasons in Satsuma . Flowers were induced in trees grown at 15 °C for 45 days and there was no induction in trees grown at 25 °C (Nishikawa et al. 2007, 2009) indicating a critical role of low temperature in inducing floral buds.

Water stress and cold conditions are the main flower induction and regulating factors. Under subtropical conditions, cold plays a major role while in tropical conditions, water stress is the key factor. Flower bud induction requires several weeks below 25 °C (Inoue 1990) as reported by Nishikawa et al. (2007, 2009) in cv. Satsuma . Similarly, a drought period (4–5 weeks) during winter season is required to induce heavy bloom and flowering intensity is directly proportional to the intensity and duration of water stress (Southwick and Davenport 1986). Hence, one of the main reasons of low production in citrus particularly cv. Kinnow mandarin in Pakistan is intercropping of berseem, wheat and other related crops and heavy flood irrigation of fields during the winter season leading to less flowering and higher flower drop (authors’ personal observations).

Water stress is used as a main tool in regulating and forcing bloom in citrus species in many leading citrus -producing countries. Generally, trees bloom 3–4 weeks after heavy irrigation suggesting application of heavy irrigation 3–4 weeks before the onset of spring. Under subtropical conditions, microscopic bud break starts during November–December, macroscopic bud differentiation occurs in December–January and flower bud visibility and anthesis starts in late January–early March. However, there may be considerable variation in these periods due to different climatic conditions in different regions and rapid fluctuations in temperatures and rainfall patterns. Off-season flowering has been commonly observed in different parts of the citrus world at different times during the winter season. Plants normally have more leafless blooms compared with leafy blooms and later produce more fruit (Erner and Bravdo 1982). More leafless blooms are produced when low winter temperatures prevail for longer durations compared with prevalence of higher winter temperatures that lead to production of leafier blooms.

There are many other factors affecting flowering including nutrition , carbohydrates, hormones, water relations and temperature .

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