Influência da deficiência hídrica na brotação de laranjeira 'Valência' infectada por Candidatus Liberibacter asiaticus e na aquisição da bactéria por Diaphorina citri
Carregando...
Data
2022-02-14
Autores
Carvalho, Waleska Soares Gomes de
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
RESUMO – O Huanglongbing (HLB) é a doença mais devastadora dos citros. Está associada a bactérias de floema (Candidatus Liberibacter asiaticus, CLas) transmitidas por insetos (Diaphorina citri). Levantamentos anuais têm mostrado que a doença ocorre de forma irregular nas diferentes regiões do estado de São Paulo, com maiores incidências nas regiões centro-leste do que nas regiões norte, noroeste, sul e sudoeste. As causas podem estar no clima com impactos em todo o patossistema. Já foi comprovado que a temperatura afeta a planta, o patógeno e o inseto vetor. Neste trabalho procurou-se quantificar o impacto do déficit hídrico (DH). O estudo foi conduzido com mudas de 4 anos de laranjeira ‘Valência’ sobre o porta-enxerto citrumelo ‘Swingle’ em casa de vegetação e sala com fotoperíodo controlado no campus da UNESP-Jaboticabal (Capítulo 2) e plantas da mesma combinação copa/porta-enxerto, com 8 anos, em pomar no município de Bebedouro (Capítulo 3). Quantificou-se o impacto do DH na brotação de plantas sadias e doentes, na multiplicação e aquisição de CLas por D. citri. Em casa de vegetação e sala as plantas foram mantidas com substrato totalmente saturado de água (sem DH), e com quantidade de água de irrigação suficiente para manter as plantas com peso total dos vasos equivalentes a 75% (DH intermediário) e 55% (DH severo) do peso das plantas sem DH. Foi quantificado o tempo necessário para surgimento e desenvolvimento dos brotos até sua completa maturação, título de CLas, e aquisição de CLas por adultos de D. citri após confinamento de adultos por 72 h. O surgimento dos brotos foi mais rápido e o tempo de maturação menor no período de temperaturas mais elevadas (julho a setembro) do que de temperaturas mais baixas (abril a junho), em ambos os ambientes. O DH não afetou o tamanho final dos brotos, que foi menor em plantas doentes, e o título de CLas nos brotos e nos insetos. Porém, o DH afetou a aquisição da bactéria. As porcentagens de insetos com CLas variou de 9,84% em plantas sob DH intermediário, 15,38% em plantas sob DH severo e 36,36% em plantas sem DH. No campo, o trabalho foi conduzido em setembro a outubro de 2020, período em que as plantas estavam sob severo DH (folhas murchas) (etapa 1), e de setembro a novembro, quando surgiram as primeiras chuvas (etapa 2), com quatro plantas por tratamento. Na etapa 1, metade das plantas foram mantidas com DH e a outra metade irrigada sob a copa com uma lâmina de 68 mm de água. Na etapa 2 as plantas foram mantidas sem irrigação com a quebra do DH proporcionado pelas chuvas. Foram quantificados a emissão e crescimento dos brotos e título bacteriano antes e após a ‘quebra’ do DH pela irrigação ou chuvas. A irrigação recuperou a turgidez das folhas das plantas sintomáticas, mas não das assintomáticas. Somente as sintomáticas emitiram brotos. No entanto, com a chegada das chuvas no mês de outubro (de aproximadamente 80 mm), 49 dias após o início do experimento, todas as plantas brotaram. A irrigação e chuvas provocaram redução tanto na incidência de brotos com CLas como no título bacteriano – de log 6 a 7 por g de tecido nas plantas sob severo DH para log 3 a 4 após irrigação ou chuvas. Conclui-se que as menores incidências de HLB nas regiões norte e noroeste do estado de São Paulo podem ser o resultado, ao menos parcial, da menor taxa de aquisição de CLas por D. citri antes e depois da quebra do DH, muito comum naquelas regiões.
ABSTRACT – Huanglongbing (HLB) is the most devastating citrus disease. It is associated with phloem bacterium (Candidatus Liberibacter asiaticus, CLas) transmitted by Diaphorina citri. Annual surveys have shown that the disease occurs irregularly in different regions of the state of São Paulo, with higher incidences in the central-east regions than in the north, northwest, south and southwest. The causes can be in the climate with impacts on the entire pathosystem. Temperature has already been proven to affect the plant, the pathogen and the insect vector. In this work we tried to quantify the impact of water deficit (WD) on 'Valencia' sweet orange plants grafted onto the 'Swingle' citrumelo rootstock in a greenhouse and room with controlled photoperiod at the UNESP-Jaboticabal campus (Chapter 2) and plants of the same scion/rootstock combination, 8 year old in an orchard in the municipality of Bebedouro (Chapter 3). The impact of WD on flushing of healthy and diseased plants, on the multiplication and acquisition of CLas by D. citri was quantified. In the greenhouse and acclimatized room, the plants were maintained with a substrate fully saturated with water (without WD), and with sufficient amount of irrigation water to maintain the plants with a total weight of the pots equivalent to 75% (intermediate WD) and 55% (severe WD) from the weight of plants without WD. The time required for flush emergence and development until complete maturation, CLas titer, and acquisition of CLas by adults of D. citri after confinement of adults for 72 hours were quantified. The emergence of shoots was faster and the maturation time was shorter in the period of higher temperatures (July to September) than of lower temperatures (April to June), in both environments. WD did not affect final shoot size, which was smaller in diseased plants, and CLas titer in shoots and insects. However, WD affected the acquisition of the bacterium. The percentages of insects with CLas ranged from 9.84% in plants under intermediate WD, 15.38% in plants under severe WD and 36.36% in plants without WD. In the field, the work was carried out from September to October 2020, when the plants were under severe WD (wilted leaves) (step 1), and from September to November, when the first rains appeared (step 2), with four plants per treatment. In step 1, half of the plants were maintained with WD and the other half irrigated under the canopy with a water depth of 68 mm. In step 2, the plants were kept without irrigation with the drop in WD provided by the rains. The emission and growth of shoots and bacterial titers were quantified before and after the WD 'break' by irrigation or rainfall. Irrigation restored leaf turgidity in symptomatic plants, but not in asymptomatic ones. Only the symptomatic ones emitted buds. However, with the arrival of rains in October (approximately 80 mm), 49 days after the beginning of the experiment, all plants sprouted. Irrigation and rainfall reduced both the incidence of shoots with CLas and bacterial titer – from log 6 to 7 per g of tissue in plants under severe WD to log 3 to 4 after irrigation or rainfall. It can be concluded that the lower incidences of HLB in the north and northwest regions of the state of São Paulo may be the result, at least partially, of the lower rate of acquisition of CLas by D. citri before and after the WD break, very common in those regions.
ABSTRACT – Huanglongbing (HLB) is the most devastating citrus disease. It is associated with phloem bacterium (Candidatus Liberibacter asiaticus, CLas) transmitted by Diaphorina citri. Annual surveys have shown that the disease occurs irregularly in different regions of the state of São Paulo, with higher incidences in the central-east regions than in the north, northwest, south and southwest. The causes can be in the climate with impacts on the entire pathosystem. Temperature has already been proven to affect the plant, the pathogen and the insect vector. In this work we tried to quantify the impact of water deficit (WD) on 'Valencia' sweet orange plants grafted onto the 'Swingle' citrumelo rootstock in a greenhouse and room with controlled photoperiod at the UNESP-Jaboticabal campus (Chapter 2) and plants of the same scion/rootstock combination, 8 year old in an orchard in the municipality of Bebedouro (Chapter 3). The impact of WD on flushing of healthy and diseased plants, on the multiplication and acquisition of CLas by D. citri was quantified. In the greenhouse and acclimatized room, the plants were maintained with a substrate fully saturated with water (without WD), and with sufficient amount of irrigation water to maintain the plants with a total weight of the pots equivalent to 75% (intermediate WD) and 55% (severe WD) from the weight of plants without WD. The time required for flush emergence and development until complete maturation, CLas titer, and acquisition of CLas by adults of D. citri after confinement of adults for 72 hours were quantified. The emergence of shoots was faster and the maturation time was shorter in the period of higher temperatures (July to September) than of lower temperatures (April to June), in both environments. WD did not affect final shoot size, which was smaller in diseased plants, and CLas titer in shoots and insects. However, WD affected the acquisition of the bacterium. The percentages of insects with CLas ranged from 9.84% in plants under intermediate WD, 15.38% in plants under severe WD and 36.36% in plants without WD. In the field, the work was carried out from September to October 2020, when the plants were under severe WD (wilted leaves) (step 1), and from September to November, when the first rains appeared (step 2), with four plants per treatment. In step 1, half of the plants were maintained with WD and the other half irrigated under the canopy with a water depth of 68 mm. In step 2, the plants were kept without irrigation with the drop in WD provided by the rains. The emission and growth of shoots and bacterial titers were quantified before and after the WD 'break' by irrigation or rainfall. Irrigation restored leaf turgidity in symptomatic plants, but not in asymptomatic ones. Only the symptomatic ones emitted buds. However, with the arrival of rains in October (approximately 80 mm), 49 days after the beginning of the experiment, all plants sprouted. Irrigation and rainfall reduced both the incidence of shoots with CLas and bacterial titer – from log 6 to 7 per g of tissue in plants under severe WD to log 3 to 4 after irrigation or rainfall. It can be concluded that the lower incidences of HLB in the north and northwest regions of the state of São Paulo may be the result, at least partially, of the lower rate of acquisition of CLas by D. citri before and after the WD break, very common in those regions.
Descrição
Palavras-chave
Estresse hídrico, Condições ambientais, Citrus, Floema