Indução de resistência por Bacillus amyloliquefaciens e Lactobacillus paracasei à Phytophthora nicotianae em porta-enxertos de citros
Resumen
Citriculture is one of the most important crops influencing the agricultural trade
balance. It is estimated that half of the orange juice consumed in the world is
produced in Brazilian orchards. In the last years the citriculture has been
suffering from many risk factors, such as high incidence of pests and diseases.
The introduction of Huanglongbing in Brazil raised the costs of spraying in the
last years, besides leading to the eradication of several citrus trees. Thus, the
replacement of these threes has made seedlings the main input in citriculture. In
nursery seedlings, Phytophthora spp. Pathogens that causes citrus gummy are
of great importance, but difficult to control because there are few effective active
ingredients. The biological control has been showing good results in controlling
these diseases using antagonistic bacteria, although stills incipient. Thus, the
aim of this study was to evaluate the ability of the two bacterial
isolates Lactobacillus paracasei and Bacillus amyloliquefaciens in inducing the
production of phenolic compounds and activating defense enzymes of two citrus
rootstocks Phytophthora nicotianae. Seeds of Citrus sunki and Poncirus
trifoliata, susceptible and resistant to P. nicotianae, respectively, were
microbiolized with the bacteria in three assays. The substrate was inoculated
with the phytopathogen at 75 days after sowing (assay 2), and the lap region
was inoculated at 90 days after sowing (assay 3). The plant shoot was used to
quantify the enzymes polyphenoxidase (PPO), peroxidase (POD),
phenylalanine ammonia-lyase (PAL) and phenolic compounds. P. sunki plants
non-inoculated with P. nicotianae (assay 1) showed higher levels of enzymatic
activity of all enzymes, except POD, and plants inoculated with B.
v
amyloliquefaciens presented high activity of PAL and PPO. Plants inoculated
with L. paracasei showed higher concentration of phenolic compounds. All C.
sunki grown in substrate inoculated with P. nicotianae presented an increased
in the enzymatic activity. PPO and PAL showed higher level of activity in the
treatments with the bacteria, and there was accumulation of phenolic
compounds. In P. trifoliata there was high activity of POD in plants treated with
B. amyloliquefaciens. High activity if PAL was observed after inoculation by P.
nicotianae in all treatments. C. sunki plants inoculated in lap region (assay 3)
showed higher severity, and presented higher activity of POD and concentration
of phenolic compounds when treated with B. amyloliquefaciens. In conclusion,
L. paracasei and B. amyloliquefaciens activated the defense system of citrus
plants, however the enzymatic activity depends on the variety of the rootstock
and if the plants were inoculated with the phytopathogen.