The purpose of this study was to better understand the interactive impact of two soil-borne pathogens, Phytophthora cactorum and Armillaria gallica, on seedlings of silver birch (Betula pendula Roth.) subjected to stress caused by mechanical defoliation, simulating primary insect feeding. This is the first experimental confirmation of silver birch seedling root damage (and in consequence shoot mortality) caused by the additive effect of defoliation stress and P. cactorum inoculation via soil. However, the most severe damage to roots occurred after A. gallica inoculation. One year after treatments, chlorophyll fluorescence measurement, and gas chromatography coupled with mass spectrometry (GC-MS) were used to analyze the photosynthetic activity in leaves, the volatile organic compounds (VOCs) emitted by the birch leaves, and chemical compounds from the roots. The cumulative effect of the two pathogens and partial defoliation reduced photosynthetic activity, suggesting dysfunction of photosystem PSII due to the applied stresses. In summary, it seems that the main differences in photosynthetic performance could be attributed to Armillaria infection. The birch leaves in seedlings exposed to 50% defoliation, and inoculation with P.cactorum and A. gallica, emitted more aromatic carbonyls and alcohols, as well as half as much aliphatic esters, compared to controls. In infected birch roots, the production of phenols, triterpenes, and fatty alcohols increased, but fatty acids decreased. Higher levels of aromatic carbonyls and alcohols in leaves, as well as phenolic compounds in the roots of stressed birches (compared to control) suggest an activation of plant systemic acquired resistance (SAR).

RESUMO: Objetivou-se verificar a influência da soma térmica e dos graus-dia negativos acumulados sobre o acúmulo de sólidos solúveis na cana-de-açúcar. O experimento foi conduzido em uma área experimental da usina Centro álcool, no município de Santo Antônio de Goiás-GO. Os dados de temperatura do ar foram obtidos da estação meteorológica automática da Escola de Agronomia da UFG (Goiânia-GO) e os sólidos solúveis determinados pelas medidas de °BRIX coletados em campo, com quatro repetições. A coleta de dados iniciou-se três meses antes da colheita correspondente ao estádio de maturação da cana-de-açúcar. A partir dos dados de temperatura (máxima, mínima e média) do ar foram calculados a soma térmica e os graus-dia negativos acumulados. Os dados foram submetidos à análise de correlação (α = 0,05). A taxa de graus-dia negativos acumulados foi decrescente, enquanto a taxa da soma térmica aumentou, isto ocorreu devido ao período das coletas (julho a setembro), em que há um aumento gradativo da temperatura do ar. Ainda assim, o aumento dos sólidos solúveis na calda da cana-de-açúcar ocorreu com o acúmulo dos graus-dia negativos (r = 0,8687; α = 0,05) apresentando um comportamento linear (R² = 0,7547).

The purpose of this study was to better understand the interactive impact of two soil-borne pathogens, Phytophthora cactorum (as the primary pathogen) and Armillaria gallica (as secondary), on two-year-old seedlings of silver birch (Betula pendula) subjected to stress caused by mechanical defoliation simulating primary insect feeding. One year after treatments, the chlorophyll fluorescence measurement and gas chromatography coupled with mass spectrometry (GC-MS) were used to analyze the photosynthetic activity in leaves, the volatile organic compounds (VOCs) emitted by birch leaves and chemical compounds from roots. Only the infection of roots by P. cactorum increased photosynthetic rates in the leaves, which may suggest its cryptic development in contrast to fungi. The birch leaves in seedlings exposed to 50% defoliation, inoculation with P. cactorum and A. gallica emitted more aromatic carbonyls and alcohols, as well as half as much aliphatic esters, compared to untreated controls. In infected birch roots, the production of phenols, triterpenes and fatty alcohols increased, but fatty acids decreased. This was the first experimental confirmation of the pathogenicity of P. cactorum on silver birch seedlings in Poland. The most severe damage to roots took place only in the case of two-way or three-way interactions. Higher levels of aromatic carbonyls and alcohols in leaves, as well as phenolic compounds in roots of stressed birches (compared to control) suggest an activation of plant systemic acquired resistance (SAR).