Photosynthesis and associated metabolism during development of a Theobroma cacaco hybrid with the lethal factor Luteus-Pa

The recessive lethal character Luteus-Pa, expressed as a yellowing of leaves of young seedlings and followed by death approximately 60 d after emergence, presents a 3:1 segregation in crosses and/or selfpollinated plants. We evaluated quantitatively the fluorescence emission of chlorophyll (Chl), gas exchange, and chemical composition of normal and recessive homozygous cacao seedlings of the cross Pa 121 x Pa 169. There were variations in Chl fluorescence, gas exchanges and chemical composition of different parts of both types of seedlings. However, no significant differences were found in the Chl distribution through photosynthetic complexes of 32-d-old normal and recessive homozygous seedlings. After that period a decrease in the Chl concentration was observed in the recessive seedlings, and only minimum fluorescence (F0) was found. The F0 values were higher in the recessive seedlings than in the normal ones. The net photosynthetic rate of mature leaves was negative in agreement with low conductance, transpiration rate, and high internal CO2 concentration.