Research develops the first guava rootstock resistant to root-knot nematode

Pioneering research by Embrapa Semiárido (PE) resulted in the development of the BRS Guaraçá rootstock, the first cultivar resistant to root-knot nematode (Meloidogyne enterolobii), the main pathogen of guava in Brazil. The technology is now available to producers, who can purchase seedlings through nurseries accredited by Embrapa.

The rootstock was generated after ten years of research, which involved the selection and evaluation of hundreds of guava and araçazeiro genotypes (a wild plant from the same family as guava trees), collected throughout the country, as well as the work of crossing plants and genetic improvement.

The BRS Guaraçá cultivar, a hybrid resulting from this crossing, has high resistance to root-knot nematodes and compatibility with most commercial guava varieties, such as Paluma, Suprema, Pedro Sato, Rica, Século XXI and those from the Cortibel group. The studies were conducted by Embrapa researchers Carlos Antonio Fernandes Santos, José Mauro da Cunha e Castro and José Egídio Flori.

The results in the field showed that the technology presents good grafting and canopy development, in addition to producing around 40 tons of fruit per hectare, in harvests carried out 30 months after transplanting, explains Santos.

With the rootstock, it is possible to manage production in areas previously infested by the nematode, once again making it possible to exploit the crop in these locations. The dissemination of technology among producers can help Brazil return to its status as a major global guava producer, circumventing the impact that root-knot nematodes caused to national production of the fruit.

Nematode gradually reduces guava production

Businessman José Mauro da Silva, from the accredited nursery Sítio São João II, in Taquaritinga-SP, believes that BRS Guaraçá “can save guava culture in Brazil”. He reports that, in most crops attacked by the nematode, productivity drops year after year, even if the producer uses palliative methods to contain the problem. “At one point, farming becomes unviable. Producers who really know the problem and already know about Embrapa's technology don't wait until the end to start planting,” reports the nurseryman.

He also points out that, even when cultivating in areas where there are still no reports of nematodes, the risk of contamination is high due to the traffic of vehicles, machinery, implements, harvesting material and the workers in the area themselves. “Currently, it is very difficult to contain the plague. However, it is possible to live with it if the orchard is formed by seedlings using the BRS Guaraçá cultivar as rootstock”, he adds.

Impact of the nematode on guava crops

Guava occupies the 11th position as the most economically important fruit in Brazil, with a production value of almost 800 million reais in 2018. (IBGE, 2020). The states of Pernambuco, São Paulo, Paraná, Bahia, Minas Gerais and Ceará, respectively, are the largest producers of the fruit.

The first commercial crops in the country began in the 70s, with strong growth over the years. In 2002, however, there was a major drop in production. This milestone coincides with the first report, which occurred in 2001, related to the presence of root-knot nematode in irrigated guava trees in the states of Pernambuco and Bahia. In subsequent years, the nematode was detected in another 18 states, becoming one of the main challenges facing culture in Brazil.

Responsible for losses exceeding 400 million reais in recent years, the nematode is widely disseminated throughout the country, currently being registered in all states where guava is produced. Abroad, there are reports in India and Mexico. In addition to guava, it attacks several other crops such as tobacco, peppers and okra.

As the name suggests, the root-knot nematode leads to the thickening of the roots and the formation of galls, which disturb the physiology of the plant and, in the case of guava, lead to the death of the plant in a relatively short period, explains Castro.

“When the nematode infects the roots of the guava tree, it injects toxic substances while sucking nutrients from the sap. It becomes a competitor of the plant in its fruit production process. Furthermore, infection of the roots by the nematode opens the door for the entry of other pathogens, such as the fungus Neocosmospora falciformis (syn. Fusarium solani), which causes root rot.”

Currently, the BRS Guaraçá rootstock is the only viable option for controlling root-knot nematode in guava in Brazil. Biological control methods, integrated management and application of insecticides have limited or inefficient results for controlling this pathogen, highlights Santos.

It is important to highlight, however, that the rootstock is not immune, but has very high resistance to the nematode. “The root system of BRS Guaraçá is not exempt from the formation of galls, but when this happens, they are formed in much smaller numbers, which do not compromise production”, adds Castro.

Opinion of the productive sector

Although commercial plantings are still recent, the performance of cultivars using the BRS Guaraçá rootstock in areas contaminated by the nematode has been quite satisfactory, according to reports from the production sector.

For Haroldo de Carvalho Neves (photo on the left), owner of the São Francisco Mudas nursery, in Petrolina (PE), the technology is decisive for the São Francisco Valley region, “which has predominantly sandy soils, where nematodes arrive very early and they degrade quickly.”

The nursery began selling BRS Guaraçá at the end of 2021, when the mother plants were acquired from Embrapa. In 2022, 28 thousand seedlings were made available to producers and by 2023, the expectation is to reach 80 thousand seedlings sold.

“BRS Guaraçá gave a huge increase to the development of production here in the Valley. There is already a lot of demand, people are getting to know the rootstock and the trend is growing, we are even sending grafted seedlings to other states by air transport”, reveals the nurseryman.

One of the satisfied producers is Antônio Carlos Rodrigues, from the municipality of Casa Nova, in Bahia. He planted Paluma seedlings grafted onto BRS in a small area and is already heading towards the third harvest. “I initially put 300 plants to test and I’m having good results. It is a resistant material, which has good production and also manages similar to that of plants that are not grafted”, he reports.

The activity was so successful that the farmer has already started expanding the area. ‘I recently planted another 400 seedlings using the rootstock. They all got it the first time. So far, I don’t have any problems with nematodes,” he declares.

The importance of purchasing quality seedlings

The researchers emphasize that, for the success of the activity, it is very important that the producer is aware of purchasing seedlings grafted onto BRS Guaraçá. The cultivar was licensed by Embrapa to six nurseries, three in Pernambuco, one in Espírito Santo, one in Paraná and one in São Paulo. The listing can be found on the Company’s website. These are the only ones authorized to reproduce the material, which is a hybrid and therefore does not multiply by seeds, highlights Embrapa's asset manager, Rodrigo Flores (on the left in the photo alongside).

In order for the producer to have the security of acquiring seedlings formed on the rootstock originating from the Embrapa matrix and, therefore, with genetic quality, the entire sales and purchase process must be documented, accompanied by the invoice and the compliance statement. “Any seedling that does not have this documentation is subject to fines, seizure and destruction, applicable both to those who sell it and to those who purchase unofficial material”, warns Flores.

In this sense, supervision is very important to reduce the source of unlicensed materials. In case of doubts regarding the origin of the material to be purchased, the producer must contact Embrapa through the Citizen Assistance Service (SAC).

The research process

The BRS Guaraçá cultivar is a hybrid plant, which mixes characteristics of guava (Psidum guajava) and araçazeiro (P. guineense), to be used as a rootstock. The crossing contains 50% of the guava genome, which minimizes incompatibility with canopy cultivars, mainly due to the small size of the araçazeiro.

The research began in 2007 with the aim of finding a guava or araçazeiro that was resistant to the nematode. In the first stage, materials collected in different Brazilian states were evaluated, and an araçazeiro immune to the nematode was identified from Rio Grande do Sul. “However, under semi-arid conditions, this araçazeiro did not develop compatibility in size with commercial cultivars of guava tree,” says Castro.

From then on, the researchers saw the need to develop a hybrid plant, which would bring to an individual the desired characteristics of resistance to the nematode and compatible size. Then began the research conducted by breeder Carlos Antonio Fernandes Santos, in a meticulous work of crossing araçazeiro with guava tree, until arriving at the hybrid BRS Guaraçá.

According to the breeder, one of the main difficulties was obtaining hybrids between Psidium species. “We carried out several manual crossings and were successful in crossing an accession of guava from Pernambuco with an accession of resistant araçazeiro, collected in Roraima”, recalls the researcher.

The research process

The BRS Guaraçá cultivar is a hybrid plant, which mixes characteristics of guava (Psidum guajava) and araçazeiro (P. guineense), to be used as a rootstock. The crossing contains 50% of the guava genome, which minimizes incompatibility with canopy cultivars, mainly due to the small size of the araçazeiro.

The research began in 2007 with the aim of finding a guava or araçazeiro that was resistant to the nematode. In the first stage, materials collected in different Brazilian states were evaluated, and an araçazeiro immune to the nematode was identified from Rio Grande do Sul. “However, under semi-arid conditions, this araçazeiro did not develop compatibility in size with commercial cultivars of guava tree,” says Castro.

From then on, the researchers saw the need to develop a hybrid plant, which would bring to an individual the desired characteristics of resistance to the nematode and compatible size. Then began the research conducted by breeder Carlos Antonio Fernandes Santos, in a meticulous work of crossing araçazeiro with guava tree, until arriving at the hybrid BRS Guaraçá.

According to the breeder, one of the main difficulties was obtaining hybrids between Psidium species. “We carried out several manual crossings and were successful in crossing an accession of guava from Pernambuco with an accession of resistant araçazeiro, collected in Roraima”, recalls the researcher.