Reduction of pineapple leaf (Ananas comosus ‘MD-2’) photosynthetic rate by the root pest Pratylenchus brachyurus

Root pests like Pratylenchus brachyurus cause great losses to the pineapple crop worldwide. However, little is known about the physiological changes that its feeding induces in the pineapple plant. The present work compared the net CO₂ assimilation rate of pineapple (Ananas comosus ‘MD-2’) plants inoculated with 504 P. brachyurus and un-inoculated plants. Plants were cultivated in sterilized soil. The net CO₂ assimilation rate was measured on the apical segment of the D-leaf with an LI-6800 portable photosynthesis system (LI-COR Environmental Sciences Inc., Nebraska USA) during the hours between 7 and 8 pm (19-20 h), 9-10 pm (21-22 h), 11-12 mn (23-24 h), 1-2 am (1-2 h) and 4-5 am (4-5h) commencing 45 days after inoculation with P. brachyurus. With exception of the 4-5 am evaluation, in all the other measurement points, a reduction between 31 and 62% of the net CO₂ assimilation rate (µmol CO₂ m^‑2 s^‑1) was found on the plants inoculated with P. brachyurus with differences at 7-8 pm (19-20 h; P=0.0059) and 9-10 pm (21-22 h; P=0.0461). When the area under the net CO₂ assimilation curve of the 5 evaluations was compared, P. brachyurus reduced (P=0.0163) the net CO₂ assimilation rate by 55.8%. Therefore, P. brachyurus alters the normal pineapple physiology causing reduced photosynthesis, which consequently can reduce pineapple yield.