Specific Gravity, Dry Matter Content, and Starch Content of Potato (Solanum tuberosum L.) Varieties Cultivated in Eastern Ethiopia

Abstract

Several farmers’ and improved potato varieties are cultivated by farmers in the eastern highlands of Ethiopia. However, sufficient information is not available on tuber quality characteristics of the potato varieties. Therefore, experiments were conducted at three locations in the region, namely, Haramaya, Hirna and Arbarakatte in eastern Ethiopia during the 2012 to 2014 main cropping season to elucidate the internal tuber quality characteristics of 17 potato varieties and prepare a specific gravity conversion chart. The treatments consisted of 17 potato varieties (Araarsaa, Badhasa, Belete, Batte, Bubu, Bulle, Chala, Chiro, Gabbisa, Gera, Gorebela, Gudanie, Guasa, Jalenie, Jarso, Mara Charre and Zemen). The experiment at location was laid out as a randomized complete block design and replicated three times per treatment. The results revealed that tuber specific gravity (SG), dry matter (DM) and starch contents (SC) were significantly influenced by variety, location and year, while the interaction of the three factors significantly influenced SG and SC. All improved cultivars produced tubers with >1.085, >21% and > 14% of SG, DM and SC, respectively, and were found to be suitable for making French fries, chips and flakes. However, tubers of the local varieties had <1.07 gcm², < 20% and < 11% SG, DM and SC, respectively, and were found to be suitable for making whole boiled potatoes. The dendrogram constructed using Unweighted Pair-group Method with Arithmetic means separated the varieties into three clusters of which Cluster I with distinct Sub-group I consisted of eight improved varieties (Ararsa, Bule, Marachere, Badhasa, Challa, Jalanine, Gabisa and Zemen) and Sub-group II six improved cultivars (Bubu, Gera, Gorbella, Gudenine, Gusa and Chiro) , and Clusters II and III consisted of one improved variety (Belete) and two farmers’ varieties (Batte and Jarso), respectively. The varieties found to be suitable for making processed potato products (French fries, etc) were grouped in the Sub-group I as they produced tubers with SG, DM and SC contents of acceptable standard for making such products while cultivars in Sub-group II and Belete (Cluster II) produced tubers with high SG, DM and SC contents that may produce too hard, dry and brittle French fries and chips. The correlation of specific gravity with dry matter and starch contents being perfect or near to perfect (r=0.962 to 1) across locations and seasons with high coefficient of determination (R²=0.924 to 0.999). It could, thus, be concluded that it is appropriate to use specific gravity and the conversion chart produced from this tuber quality trait to estimate the other two traits (dry matter and starch contents) and determine the quality of tubers for processing.

Keywords: Coefficient of determination; Conversion chart; Correlation; Internal tuber quality.