:: Fincas de Ambato :: Polinización Artificial / Introducción, Referencias, Figuras

Jojoba needs to undergo a low-temperature period for ending dormancy and allowing flower opening. As these cold-temperature needs are genetically dependent requirements, they vary for each different ecotype, as a result of which genotypes that can flower under different thermal conditions may be selected (Ayerza, 1992).

Jojoba vernalization requirements were not identified until 1989 (Ferriere et al., 1989), when commercial plantations were already in place in various tropical and subtropical ecosystems with no low-temperature periods (or with low-temperature periods too short to allow full vernalization). Between the late 1970s and mid-1990s, this caused more than 11,000 has. of jojoba to be abandoned as they proved unable of flowering in tropical areas of Argentina (2,500 has.), Brazil (4,000 has.), Costa Rica (2z100 has.), and Paraguay (3,000 has.).

Table 1-V illustrates the flowering sequence and low flowering rate for male plants originating from seed at a jojoba plantation in Nueva Asuncion (in the tropical region of Paraguay), where there is no cold season that meets the vernalization requirements applicable to virtually all jojoba genotypes.

Currently, as a result of selection works recently performed in Argentina, Colombia and Madagascar, there are genotypes that can flower and fruit in tropical and subtropical areas where the vast majority of commercially available jojoba genotypes are unable to have their minimum vernalization requirements satisfied.

Knowledge of each genotype’s vernalization requirements is not only important where tropical regions are involved, but also for future plantations in frost-prone areas. Planting genotypes with low vernalization requirements will cause them to have such requirements met early on in the cold season, thus flowering before the frost season is actually over. Closed jojoba buds can take between -4 and -8 °C, depending on their respective development stage; however, open flowers (or those in the early fruit stages) die at 0 °C.

Anthesis can be delayed through agronomical practices such as creating water stress conditions by suspending irrigation during the frost season. Even though this practice will lead to a considerable reduction in the number of flowers killed by frost, this will be accompanied by a reduction in the plant’s productive potential, depending on the degree of water stress (Nelson and Palzkill, 1995).

Water stress is a very important practice in frost-prone areas, but it is not at all a substitute for the use of genotypes with vernalization requirements that allow them to flower once the threat of frost has subsided.

Table 2-V shows the flower-opening status of 3 clones selected for blooming after the threat of frost is over (Table 4-CJ), viewed in contrast to the flowering status of wild-picked clones, and a clone selected for planting under tropical conditions. Agronomical management was identical in all cases, save for one lot of the Ambato 10 clone, for which annual irrigation started 15 days earlier than the rest.

Even though it is commonly agreed that jojoba needs daily temperatures between 13 °C and 18 °C for a period of at least 20 days for proper vernalization, this is only a general conclusion that can be used as indicative data for the possibilities of most commercially available genotypes. However, only the formulas developed by R. Dustone and P. Milthorpe in Australia allow accurate measurements for a specific area.

Table 3-V shows the potential length of the vernalization periods for every year between 1994 and 2004 at Fincas de Ambato. Calculations were based on the specific cold-temperature requirements of jojoba for achieving satisfactory flowering both as regards the number of open flowers and the duration of the anthesis period. The formula developed by Dunstone and Milthorpe (1989), as later modified by Dunstone in 1995, was used as a starting point. The de-vernalization phenomenon was only factored in for temperatures escalating above 25 °C for at least 12 hours.