MANNITOL AND OLIGOSACCHARIDES: POTENTIAL NEW CRITERIA FOR DETERMINING COLD TOLERANCE IN SUGARCANE VARIETIES

摘要

Sugarcane can be very susceptible to damage by freezes. The frequent winter freezes of Louisiana force the industry to adapt to a short growing season (7 to 9 months) and a short milling season (approx. 3 months). Freeze deteriorated cane can cause problems in processing and sometimes leads to a factory shut-down. This study was undertaken during the 2000/2001 harvest season to assess the cold tolerance performance of six commercial sugarcane varieties and to establish new and more sensitive criteria to measure cold tolerance. Two commercial varieties CP 70-321 and CP 79-318 with known cold tolerance were planted in the study as controls. The other varieties included LHo 83-153, LCP 85-384, HoCP 85-845 and HoCP 91-555. Freezing temperatures occurred on Dec 20, 2000 when the minimum field temperature was 24℉, and again on Dec 21, Dec 30 through Jan 5, 2001, Jan 9-10 and January 20-21. The lowest field temperature recorded was 22℉ on Jan 4. Freezing conditions prevailed for 8-15 hours during each freeze incident. Stalks of all varieties were frozen to the ground following the initial freeze with freeze cracks evident only after the January 4 freeze. For this study, samples were taken on the date of the first freeze, December 20, and subsequently again at 7, 14, 22 and 30 days after the first freeze. Criteria used to measure overall stalk cold tolerance included changes in pH, Brix, dextran (ASI-Ⅱ method), sucrose, glucose, and fructose concentrations. Mannitol, ethanol and the oligosaccharides palatinose, leucrose, iso-maltotriose and 1 -kestose were simultaneuously measured using IC-IPAD. Marked differences were observed for most criteria for all varieties, particularly 22 and 30 days after the first freeze. Mannitol was strongly correlated (r~2 = 0.84) with dextran confirming its use as an indicator for cane dextran or Leuconostoc deterioration. In comparison, ethanol was only weakly correlated (r~2=.55) with dextran and did not always predict cane dextran deterioration. Iso-maltotriose was the most sensitive oligosaccharide indicator of freeze deterioration, although both leucrose and palatinose could be used to confirm if severe dextran formation (>1500ppm/Brix) has occurred in cane. Iso-maltotriose was strongly correlated (r~2 = 0.89) with dextran and pH (r~2= 0.91). pH was also a strong indicator of both dextran (r~2 = -0.85) and mannitol (r~2 = - 0.92) formation. Four of the varieties, CP 79-318, LCP 85-384, HoCP 85-845 and HoCP 91-555, were shown to be susceptible to other sources of microbial and enzymic deterioration as well as dextran deterioration from Leuconostoc bacteria, especially 30 days after the first freeze. This was indicated by increased glucose/fructose ratios, ethanol formation, changes in 1-kestose concentration, and further sucrose losses.