Chipping quality of potatoes stored in heaps and pits in subtropical plains of India

Two potato cultivars Kufri Bahar and Kufri Jyoti were stored in heaps and pits under ambient conditions of sub-tropical plains of northern India and their chipping quality was determined after 90 days of storage. During storage there was a significant reduction (33.84%) in the reducing sugar content of potatoes and improvement (31.63%) in chip colour. Sugar levels in stored potatoes were within the acceptable limit for processing and table purposes indicating that potatoes stored up to 90 days on the farm in heap and pits are suitable for these two purposes.  

Environmental Stressors That May Influence Internal Heat Necrosis in Potato Production in Northeast Florida

`Atlantic' potatoes (Solanum tuberosum L.) are grown on approximately 8100 hectares with seepage irrigation in Northeast Florida's Tri-County Agricultural Area (St. Johns, Putnam, and Flagler counties). `Atlantic' is preferred for its chipping quality, high specific gravity and yield, but is susceptible to internal heat necrosis (IHN), a physiologic disorder that affects potato tuber quality. The relationships of environmental stressors (growing degree days, GDD and rainfall) to IHN were evaluated on two fields (fields 3 and 4) on a local producer's farm. IHN reduced marketable tuber yield by 100% in the 1995 and 2003 seasons, but not in 2001 and 2002 seasons. From 3 to 6 weeks after planting (WAP), GDD for 1995, 2001, 2002, and 2003 were 470, 325, 386, and 628 (45° F base), respectively. This is the only 4 week period during the 14 week season that GDD accumulation by week was different among treatments. Average rainfalls (cm) for the same periods were 1.60, 1.12, 2.23 and 7.91, respectively. Both warmer/dryer and warmer/wetter early season conditions occurred during seasons with higher rates of IHN. Although circumstantial, higher accumulated heat units and water stress within the first 6 weeks of the growing season resulted in higher percentages of tubers with IHN. These relationships should be evaluated further with other growers.

Comparative performance of three test methods for determining chipping quality in tubers of potato (Solanum tuberosum L.)

The capacity of a colour chart and a reflectance photometer (Agtron) to accurately determine chipping quality of potato tubers was assessed using data sets taken over a 4-yr period for 17–32 cultivars. Both tests gave a high diagnostic accuracy for chipping quality regardless of sampling time from storage or the occurrence of high temperature reconditioning when evaluated by receiver operating characteristic (ROC) curve analysis. Receiver operating characteristic curve analysis showed that both tuber glucose content and chip colour provided good diagnostic performance in correctly separating processing from non-processing tubers over a range of growing and storage conditions. Identification of chipping from non-chipping tuber samples from a 13 °C storage across a range of cultivars and growing conditions occurred with a minimum chipping colour threshold range of 41–47 or a maximum glucose concentration range of 4.3–5.4 mmol L−1 of tuber cell sap. The practical value of a test can depend on such factors as prevalence of chippers in a tuber population as well as the cost of misclassifications, i.e., costs associated with false positive or false negative test results and expressed in relative terms as the unit cost ratio. An examination of Prevalence-Value-Accuracy (PVA) plots for one of the data sets indicated that total misclassification costs could increase rapidly, depending on the prevalence of chipping tubers and the relative amounts of false negative and false positive costs. Maximum costs were consistently associated with a prevalence of 50% chippers and a unit cost ratio of 0.5. In a tuber sample containing a high prevalence of chippers (50–70%) and a low unit cost ratio (<0.2), an acceptable colour threshold determined by PVA-Threshold (PVAT) plots would be approximately 40 to 50 from the Agriculture and Agri-Food Canada colour chart. However, if the colour chart was used for screening tuber samples with a low prevalence (20–40%) of chippers and a unit cost ratio >0.20, a threshold between 60 and 65 would be optimum. The latter range would be conservative and agrees with, and supports, current industry standards, which reside at 60 or better. Since a good diagnostic test should be repeatable and subject to minimal inter-observer variation, the more objective glucose or reflectance photometric tests may be preferable and provide acceptable diagnostic accuracy for processing quality. However, the present study indicates that all three test methods are acceptable for accurately separating chipping from non-chipping tubers regardless of sampling or storage protocols. Key words: Potato, colour chart, reflectance colorimetry, glucose content

Genetic components of potato chip quality evaluated in three environments and under various storage regimes

A diallel series of crosses was made between parents with good processing quality and nonprocessing but well-adapted varieties and breeding clones to study the inheritance of chipping quality and tuber yield in potatoes. The progeny of the crosses were assessed in three widely differing growing environments and chipped from a range of storage environments. Principal component analysis for chip color indicated that the first (PCA1) and second (PCA2) principal components accounted for 84.4 and 5.0% of the total variability, respectively. PCA1 scores were highly correlated (P < 0.01) with the mean chip color scores of the 20 crosses measured over the 11 environments, whereas PCA2 scores were highly correlated (P < 0.01) with the standard deviations of the chip scores over storage environments. These results provide new information that supports the recently proposed concept of two genetically independent systems determining chip color, i.e., "overall chipping quality" and "chipping stability". Highly significant (P < 0.01) general combining-ability and nonsignificant specific combining-ability effects suggest additive genetic factors and high narrow-sense heritability for specific gravity. Combining-ability effects for yield traits were generally nonsignificant, which probably reflects the selection of parents with proven breeding value.Key words: Solanum tuberosum, stability, yield, specific gravity