The growth, development and yield of seven cultivars were evaluated under field conditions with photoperiods from 11.5 to 16 hours and light intensities from full light (≧12 MJ/m2/day) to only 42% light in in 3 experiments in the Philippines. The longer photoperiod significantly delayed and reduced tuberization, promoted profuse haulm growth, resulting in: more branching, increased plant height, more flowering, many secondary stems and delayed plant senescence. ‘DTO-33’ was least affected by long photoperiod, followed by ‘Red Pontiac’ and ‘Désirée’. Shading resulted in delayed tuber initiation, taller plants, thinner stems, smaller leaves but longer canopy duration and a slightly larger canopy. ‘DTO-33’ was least affected by shading followed by ‘Désirée’, ‘LT-2’ and ’Red Pontiac’. ‘LT-5’ and ‘P-3’ suffered the greatest tuber yield reduction through shading.
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