Effect of temperature on inflorescence and floral development in four mango (Mangifera indica L.) cultivars

To study the effect of low temperature on inflorescence and floral developm ent of mango (Mangifera indica L.), 'Nam Dok Mai', 'Kensington', 'Irwin' an d 'Sensation' trees were exposed to natural winter temperatures to induce f lowering, and then transferred to controlled-environment glasshouse rooms w here day/night temperature regimes of 15/5 degrees, 20/10 degrees, 25/15 de grees and 30/20 degrees C were maintained for 20 weeks. Day/night temperatu res of 15/5 degrees C severely inhibited the emergence and elongation of in florescences of all cultivars with inflorescence development only occurring on trees that were maintained at the warmer temperatures (20/10 degrees, 2 5/15 degrees and 30/20 degrees C). The time taken for inflorescences to rea ch maximum length was 15-20 days on trees held at 25/15 degrees or 30/20 de grees C but extended to 54 days on trees kept at 20/10 degrees C. Warmer te mperatures generally increased the inflorescence size of all cultivars, At 20/10 degrees C, pollen viability of 'Sensation' was significantly lower th an the other cultivars, but there was no significant difference between cul tivars held at 25/15 degrees and 30/20 degrees C, Low temperatures caused m orphological changes in styles, stigmas, ovaries and anther size in all cul tivars, and changes were especially pronounced in 'Kensington'. Style lengt h and stigma width of all cultivars were reduced when trees were held at 20 /10 degrees C compared to trees field at either 25/15 degrees or 30/20 degr ees C. Trees of 'Kensington' grown at 20/10 degrees C mainly produced flowe rs that had short styles (0.62 mm) and small stigmas (0.09 mm) while 'Nam D ok Mai' and 'Irwin' trees produced some flowers with deformed or fused ovar ies. Scanning electron microscopic studies indicated that normal 'Kensingto n' flowers had non-symmetrical stigmas that were covered with undeveloped p apillae cells. The short-styled 'Kensington' flowers (produced at 20/10 deg rees C) had a much smaller receptive stigmatic area compared to normal flow ers produced at 30/20 degrees C. Low temperature-induced (20/10 degrees C) changes in ovary size in 'Nam Dolt Mai' and style length in 'Kensington' fl owers may contribute to low fruit set in these two cultivars when grown in subtropical climates. (C) 1999 Elsevier Science B.V. All rights reserved.