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Basic menu with quality

Researchers carry out studies on genetic selection and control of the diseases that promise to make bean growing more productive

eduardo cesar

Samples from the Germplasm Bank of the IACeduardo cesar

One of the main sources of protein, and often the only one, in the Brazilian diet, beans are an indispensable ingredient in the food basket and on the menu of the population, particularly for the poorer classes of society. According to the Brazilian Agricultural Research Corporation (Embrapa), each inhabitant consumes an average of 16 kilos of beans a year, which makes Brazil the world’s largest producer and consumer of pulses of the Phaseolus vulgaris species. The importance of this food underlines the merit of two innovative studies, carried out with the support of FAPESP.

They are the thematic project coordinated by Armando Bergamin Filho, from the Luiz de Queiroz College of Agriculture (Esalq-USP), the research benefit for Sérgio Augusto Morais Carbonell, from the Center for Grain-bearing Plants of the Agronomic Institute of Campinas (IAC). They are working hard, respectively, on carrying out studies on plant pathology and the genetic improvement of the bean plant.

The challenge for Bergamin, Esalq’s professor of Plant Pathology, is to draw up a methodology that may in future enable farmers to follow a safe calendar for applying agro-chemicals in the area of bean growing, as it already happens with other crops of grain, like soya, wheat and corn. Carbonell is developing a new selection of bean varieties that are disease resistant, more specifically to anthracnose, a disease that causes necrosis in all the parts of the plants exposed to air, including the grains, and whose infectious agent is the Colletotrichum lindemuthianum fungus.

Carbonell’s studies also cover the development of strains with a better technological and culinary quality. The major concern of these researchers – in spite of the different lines of work – is the high disease incidence in crops, particularly anthracnose. Other important diseases that attack the bean plant are the angular leaf spot caused by the Phaeoisariopsis griseola fungus, and the common bacterial blight with the Xanthomonas axonopodis pv. phaseoli bacterium.

“These diseases hit the leaves and the pods of the plant, affecting the quality of the grain, and causing losses of as much as 30% to 40% of agricultural production – in some cases, they may lead to a total loss”, says Bergamin. “Furthermore, the pathogens can be transmitted through the seeds, which damages not only the crop directly affected, but also the following harvests”, Carbonell adds.

Phytosanatary control
Besides the three main diseases of the bean plant, Bergamin is also investigating the action and control of the rust caused by the Uromyces appendiculatus fungus, and of the golden mosaic of the bean, caused by a virus of the geminivirus family, Bean Golden Mosaic Virus (BGMV), which is transmitted by the tobacco whitefly (Bemisia tabaci). Rust causes circular lesions on the leaves of the bean plant, surrounded by a yellowish halo, and the golden mosaic affects the whole plant systemically.

“The golden mosaic has a strong incidence in Paraná, where there are many crops of soya. The whitefly lives in these plantations, and at certain times of the year it is totally out of the question to grow beans in this state, since between 80% and 100% of the crops are destroyed by the mosaic”, he says. Carbonell reports that in São Paulo the period with the highest incidence of this disease in the crops runs from February to May.

Until now, the bean producers’ problem has been to define the exact moment to spray the pesticides. “If spraying does not take place in time, these diseases causes losses of at least 30% of the crop”, Bergamin reveals. But most farmers follow a fixed calendar for spraying , by which the plantation is treated two to six times a crop, even when there is no risk of infection in the crop, or just sprays the area when the disease has reached a certain level. “In the first case, besides the high cost of pulverization, this is a practice that pollutes the environment, as the pesticides are reasonably toxic. The second alternative, on the hand, does not work as well for beans as for other cereal crops: the disease can apparently be at a low level, but the damage to the plant’s physiological functions may be irreparable”.

To calculate the so-called “damage threshold”, the point in the fall in production breaks even with the amount invested in pesticides, and from there on, spraying is necessary for the farmer to avoid a loss -, agronomists use the technique of measuring the leaves area affected by the diseases. “The larger the diseased leaf area, the greater the fall in production, which can be demonstrated in graphs, but not in the case of beans”, says Bergamin. This procedure is widely used in the cereal belts of the United States, especially for the wheat and corn crops, where there is a direct relation between the diseases severity and the loss of production of the plants.

New approach
Several attempts to adapt this methodology to the bean agribusiness in Brazil have ended up in failure, as there is no mathematical relation between the measurements of the diseased area of the leaf and the level of production. Bergamin set out on a new approach and started to measure the remaining leaf area. 12 field tests were carried out with the pink and ‘carioca’ varieties of the bean.

The stratagem worked, and this was how it became possible to calculate in graphs the damage threshold for the bean plant. “We started from the finding that the growth of leaves of the plant varies between 20 and 60 leaves, and so an irregular number that differs from the most cultivated cereals, which have a certain number of leaves”, reveals Lílian Amorim, from Esalq. “The measurement of the diseased area did not take this into account.” Turning the logic around, the team from Esalq demonstrated that the larger the remaining leaf area, the greater the production.

Besides recording the size of the healthy leaf area, the researchers decided to measure photosynthetic efficiency as well, or RUE, Radiation Use Efficiency, which would make it possible to assess the extent of the damage caused by the diseases to the leaves and pods. “We needed to discover if the diseases were limited to the area of the leaf that is visibly diseased, or if they also affected the area surrounding the stricken point”, says Lílian. To do so, a chamber showing the exchange of gases was used, which measures how much CO2 is absorbed by the leaves, and, consequently, the plant’s photosynthesis rate.With this method, the team found that anthracnose is the most harmful disease for the bean plant, as it affects a considerable area around the area where the presence of the fungus is visible.

At the other extreme, rust acts practically only at the spot where the action of the fungus is visible. The other diseases – angular leaf spot, common bacterial blight and golden mosaic – are at the mid-point, not being as harmful as anthracnose nor as bland, in this regard, as rust. The next step is to test the results found in the project in big crops, to find the best way for the farmer to apply in practice the results confirmed by the study.

Genetic improvement
Another resource that is increasingly employed in growing beans is planting strains obtained by genetic selection. There are already on the market seeds that resist some of the causal agents of the diseases of the bean plant. “Today, over 90% of the producers use strains that are genetically improved. Their seeds are two or three times more expensive than the beans used for consumption that are generally used as seeds by farmers, but the savings from the reduction in the use of pesticides, the uniformity of the plants, and the certainty that the seeds are not introducing new diseases into their properties make it worthwhile”, says Carbonell.

Between 1998 and 1999, he carried out his first project, entitled Genetic Improvement of the Bean Plant to Resist the Causal Agents of Anthracnose, Angular Leaf Spot and Common Bacterial Blight. He is now developing the second one, to supplement the previous one. Genetic improvement, however, does not replace entirely the procedure of spraying the crops, as there are still no strains of beans that are simultaneously resistant to all the diseases. Carbonell’s dream is to manage to select varieties of beans that are totally resistant to angular leaf spot, anthracnose and common bacterial blight – the three diseases that are most devastating for the Brazilian crops.

To do so, in 1996 the scientist began a daring program for genetic improvement, which had the objective of forming basic populations with multiple resistance to the pathogens, and to study their variability, as well as their aggressiveness and distribution in the state of São Paulo. Financed by FAPESP, this project was coordinated by Carbonell and developed by another four researchers from the IAC and the Regional University Center of Espírito Santo do Pinhal (SP).

The first step to make the project feasible was to set up and organize the IAC’s Germplasm Bank, which has collected over 1,200 kinds of beans of the P. vulgaris species. It was from this bank that Carbonell picked the varieties known to be resistant to at least one of the pathogens of the diseases under study to carry out the cross breeding among the bean plants. From 1996 to 1998, 134 multiple cross breedings were done, involving the various disease resisting genes – a task that is continuing, nowadays, with lineages of plants in the sixth generation.

When obtaining the second generation population, resulting from the original cross breeding, the researcher was able to select, under controlled laboratory conditions, bean plants that were resistant to all the pathogens of anthracnose. “It was the first step for the IAC to be able to produce a strain of beans resistant to the other diseases, which may reduce the use of agrochemicals in future”, he declares. The work with angular leaf spot and common bacterial blight is still bumping into difficulties, since the majority of plants continues to be susceptible to some of these pathogens.

Technological quality
In 1998, when the sequence of crossbreeding reached the fifth generation, Carbonell started his second project, with the participation of researchers from the Regional University Center of Espírito Santo do Pinhal and from the experimental agronomy stations of the IAC in the cities of Monte Alegre do Sul, Tatuí and Tietê, all from São Paulo. The purpose of this work, which is still under way, is to select the best anthracnose resistant strains, and, at the same time, plants with a better technological quality. In that same year, the Ministry of Agriculture started demanding that, besides being resistant to diseases, the genetically improved strains of beans should provide culinary quality.

From the fifth generation, with some 2,500 strains selected, the team from the IAC separated the most productive 98, with plants that stood upright, were totally resistant to anthracnose and had a high technological quality. Among these plants, 32 strains are of the ‘carioca’ kind – which accounts for some 70% of the domestic consumption of 3 million tons a year – and 19 of black beans. These plants are being tested in the field, in three São Paulo municipalities: Tatuí, Monte Alegre do Sul and Capão Bonito, areas that have different climates, to analyze the effect of the interaction of the genotype with the environment. According to Carbonell, the strains that show good performance in the three regions – both in terms of resistance and of quality – will be chosen for coming into competition in 2003, with varieties from other research institutes.

Change of habits
The IAC is a pioneer in Brazil in the programs for the genetic improvement of beans. It was there that researcher Luís Dartagnan de Almeida produced the first variety of ‘carioca’ beans, called ‘carioquinha’, launched in 1970. This variety – 30% more productive than the other varieties of beans of those days – revolutionized this crop in Brazil and took first place in the Brazilians’ preference.

The ‘carioca’ bean is now in its fourth generation, and came to include several anthracnose resistant genes in its third generation. “The fifth generation of new strains of the bean plant, resistant to anthracnose and other diseases and with high technological quality as well, is forecast to be launched in 2006, and so to set of a new revolution in our everyday beans”.

A New Approach for the Development of a Sustainable System of Handling Diseases of the Bean Plant Based on the Duration of the Health Leaf Area and on Photosynthetic Efficiency
Thematic project
Armando Bergamin Filho – Esalq/USP
R$ 238,249.30 and US$ 130,892.51
Advancement of Generations and Selection of Plants, Lines and Families of the Bean Plant (Phaseolus vulgaris L.) for High Productivity, Resistance to Anthracnose and Technological Quality
Regular research benefit line
Sergio Augusto Morais Carbonell – IAC
R$ 99,827.10 and US$ 4,636.00