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According to it published the La Naci³n newspaper the pollenizers are allied of the Argentine sunflower

According to a study of the chair of Agricultural Botany of the Faculty of Agronomy of the University of Buenos Aires (Fauba) it reveals that, even with the genetic improvements, the present hybrids depend on certain insects to maximize their yield. The investigators investigate on handling strategies to assure the presence most efficient.

Argentina is one of the main world-wide producers of sunflower, the one that is cultivated commercially from Shako to the south of Buenos Aires. Nowadays, which sowing is mainly hybrid artificial, result of a long process of improvement that lifted the percentage of oil by plant and diminished the strong self-incompatibility that the ancestors of the sunflower had, since now the flowers can fructify if they are pollinated with pollen of they themselves or of another plant of the culture.

€œNevertheless, local and international the information on pollination of the sunflower indicates that, in spite of the generalized perception, the yield of the culture can be limited by the quality of the service of pollination that the insects offer€, it explained agronomist Diego Medan, director of a UBACyT project, that investigates this subject.

The equipment of the Fauba left from a very simple premise, but not very often had in account by the producers: if there are insects that visit the chapters, pollen will arrive at the stigmata and fruits will form. On the contrary, if there are visits of no insects, there will be no pollen in the stigmata and aborted fruits will be only obtained. 

In a test to field, on 4 hectares of experimental parcels of the INTA generally Villegas, seeding with 30 different hybrids, the equipment of the Fauba pocketed some chapters and left exposed others as control.

The pocketed one reduced the rate of fruition strongly (from 90 to 66%).

€œThe experiment confirmed that a significant fraction of the yield depends on the service of the pollenizers, even though many covered flowers fructified anyway. This was to wait for since the present hybrids have improved genetically to free the sunflower from their pollenizers, but evidently this has not been obtained absolutely still€, indicated Medan.

Nevertheless, many farmers are persuaded that the present hybrids have such efficiency in their autopolinizaci³n, that the systematic installation of beehives of mel­feras bees in the neighborhoods of the culture no longer seems a generalized practice.

The scientists noticed that the suitable pollination compensates adverse factors (self-incompatibility still surplus in the commercial genotypes, morphologic barriers against the autopolinizaci³n, et cetera); a deficient pollination causes abortion of fruits and/or diminution of its oil weight and/or its tenor. To value the quality of the pollination is, then, important.

Efficient visitors

Once answered affirmatively the question by the dependency, the investigators put themselves to work to settle down what insects visit the sunflower, who among them are quality pollenizers, why they are it, and when and where they act. In this way, factors could be established that influence in the quality of the service of pollination and strategies of handling to improve it. Between 2003 and 2005, they registered and they caught the insects that visited the chapters and the surrounding weeds of the culture in different girasoleras regions from the country.

Comparing two samplings, one realised generally Villegas and another one in Balcarce, the people in charge of the study observed that, although in the first site the visits of the pollenizers were more sporadic, the visitors were also diverse and the rate of fruition more was lifted.

€œGenerally Villegas, the list of visitors was dominated by a group of native bees that seem to much more transport pollen by individual that the domestic bee. This goes to the chapters mainly in search of the nectar and lies down to discard the pollen that adheres to him to the body. We conclude that the identity of the pollenizers can as much be or more important that its frequency of visits€, explained the director of the study.

It was also considered important to analyze the structure of the network plant-pollenizer, for which they studied the interaction surrounding sunflower-visitor-weeds.

€œTo make this evaluation it is justified because the presence of the pollenizers can not depend exclusively on the resources that the culture provides. This information can lead to reframe the handling of the areas that surround to the culture, and also to recognize that the quality of the service of pollination depends as much on local factors (lot scale) as supralocal (landscape scale)€, extended Medan.

In the sample of General Villegas, the sunflower and nine weeds that were coexisting with the culture attracted 40 species of insects, of which 32.6% were himen³pteros (bees and wasps), 23.2% lepid³pteros (butterflies), 23.2% coleopters (beetles), dipterous 18.6% (compatible flies and) and 2.3% hem­pteros (bugs).

80% of the visits of the insects were concentrated in the sunflower and three of the weeds: mostacilla, the false bishop's weed and the black thistle.

The analysis of that network suggests exist plants of the surrounding vegetation (weeds) that are potentially important for the pollination of the sunflower, since they could complement the diet of the visitors of the culture and/or maintain them before or after the flowering of the sunflower.

Cord of weeds

By all this, the investigators suggest to leave a cord of weeds, fought generally by the producer, could in some sites turn out a strategy from handling to favor the pollination and, therefore, the yield.

A finding that surprised the investigators was the great diversity of moths that visit the sunflower at night. These insects only consume nectar and energy of the plant, but they do not contribute with the service of pollination.