Genetic variation

The great variability inherent in Brassica species has led to the enormous spectrum of crop types (Chapter 1). This high variability ultimately resulted in a spread of maturity periods within individual crops that caused much difficulty for growers in achieving efficient harvesting of high-quality produce. The standard means of overcoming variation in the maturity of Brassica crops is the taking of multiple harvests in which the crop is picked over by hand. Field staff assess quality and maturity visually as they walk through a crop. This is very labour-intensive and inefficient, and makes scheduling for marketing extremely difficult. Minor changes in the weather, leading to a few abnormally hot days or a more prolonged cold period, will disrupt the most carefully prepared harvesting schedules. The development of F1 hybrid Brassica crops offered a considerable advance in the control of their uniformity and reliability of maturation, and allowed the development of fully mechanized harvesting for Brussels sprouts and the use of gantry systems for crops such as cabbage, broccoli (calabrese) and cauliflower. Fully automated harvesting of fragile crops such as cauliflower is in the early phases of development. Here image analysis programs are used to assess the maturity of cauliflower curds and electronic signals are transmitted directly to automated cutting equipment when a head has been selected. These systems are relatively expensive, but this is set against the increasing problems that beset Brassica growers worldwide in locating and attracting field staff who are prepared to undertake harvesting in inclement weather at low rates of pay.

The move towards raising of transplants in modular containers by specialist propagators has considerably improved the uniformity of maturation gained from the genetic improvement pioneered by plant breeders. Propagation (Chapter 3) has been separated from crop growing, and the growing of seedlings prior to transplanting into the field is carefully controlled and regulated by specialist contractors. Standardized transplants are spaced mechanically in their field stations with accuracy and consistency. Provided soil fertility has been carefully adjusted to suit Brassica crops, then the subsequent transplants will establish quickly and form uniform root systems. Both the breeding of F1 hybrids and production of modularized transplants have been major scientific advances reducing the variation of Brassica crops in their maturity phase and increasing their quality postharvest.

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