Adaptability Study of Irish Potato (Solanum tuberosum L.) Varieties for Yield and Yield Components under Kaffa Zone, South Western Ethiopia

Potato is one of the most important food crops grown in mid and high altitude areas of Ethiopia. To meet the increasing demand of potato several potato genotypes have been introduced and evaluated at different areas of the country. However, the performances of different released potato varieties were not yet assessed in the study area. To this end, the present study was undertaken with the focus on determining the adaptability of Irish potato varieties for yield and yield components. It was conducted at Kaffa zone Adiyo District in Alarigeta experimental sub-station in 2013 and 2014 Belge cropping season. Seven improved potato varieties; namely Bule, Marachare, Wochecha, Dancha, Jallanie, Gudanie and Belete were used as treatment. Treatments were arranged in randomized complete block design with three replications. Average tuber diameter, average tuber number, average tuber weight, marketable tuber number, unmarketable tuber number, total tuber number, marketable tuber yield, unmarketable yield and total tuber yield data were recorded and submitted to SAS software version 9.0. Analysis of variance for each year showed significant (p<0.05) difference among the varieties for all studied traits except Average tuber diameter and marketable tuber number in 2013 and Average tuber diameter and unmarketable tuber yield in 2014. The highest and consistent tuber yield was found in variety Belete (40.54 t/ha and 39.98 t/ha) in 2013 and 2014 respectively. Therefore, variety Belete, which was given high yield in both years, could be used instated of currently cultivating varieties to increase production and productivity of the crop for better enhancement of food security and livelihood income of the locality.


Introduction
Potato (Solanum tuberosum L.) is one of the most important food crops in many countries of the world [1]. In volume of production it ranks fourth in the world after maize, rice, and wheat with annual production of 314.1 million tons cultivated on about 18.1 million hectares of land [1] and among the root crops, potato ranks first in volume produced and consumed, followed by cassava, sweet potato, and yam [2].
It is an important food and cash crop in eastern and central Africa, playing a major role in national food security and nutrition specially in disaster situations, poverty alleviation and income generation, and provides employment in the production, processing and marketing sub-sectors [3,4].
Potato is efficient in converting resources such as labour and capital in to a high energy food. Its efficiency of protein production is also higher than commonly realized. If carefully managed, it gives the highest yield of nourishment per hectare of all basic food stuffs in tropical countries. Furthermore, the growing period is only 90-125 days; enable multiple cropping for optimum use of the available land moisture. Hence, it is noted that in potato producing areas double cropping is possible [5].
Potato is grown for food, animal feed, industrial uses and for seed tuber production. The main use is still as direct food but, an increasing proportion is processed into snack food. Potato is important for subsistence farmers but may also be a cash crop [6].
Potato was introduced to Ethiopia in 1858 by the German Botanist Schemper. Since then, potato became an important garden crop in many parts of the country. About 70% of the available agricultural land is suitable for potato production which is located at an altitude of 1500 to 3000 m.a.s.l with an annual rainfall between 600 and 1200 mm [4]. More than 3.3 million smallholders are engaged in potato production and over 1.61 million tonnes of potato was produced in 2013/14, a 71% increase compared to production in 2008/09 [7]. According to the [8], the average potato tuber yield in Ethiopia is estimated to be 9.0 t/ha in 2013/14. Even though this increased average national yield is very low as compared with the world average potato tuber yield (17.16 t/ha) [7]. A number of production constraints that accounts for low yield have been identified in the country and which are also commonly prevailed in the study area. The major ones are lack of stable, well-adapted, high yielding, acceptable and disease resistant cultivars and using of local cultivars, which are highly susceptible to late blight that sometimes leads to 100% yield loss [9]. Improved potato varieties together with improved management proved to give three to four fold yield advantage as compared to local varieties together with traditional production and management practices [10]. Thus, testing improved potato technologies to specific areas would help to identify best fit technologies to the existing production system that can ensure sustainable food security [10]. Therefore, the experiment was amid to test the adaptability and select high yielding potato variety to increase production and productivity of the crop for better improvement of food security and self sufficiency of livelihood of the area.

Description of the study area
The experiment was conducted at Adiyo District, Alarigeta experimental sub-station in South Western Ethiopia during 2013/2005 and 2014/2006 belg cropping season. Alarigeta is 21 km away from Bonga town to South, which is 449 km south west of Addis Ababa. The site an altitude of 2474 masl and is experienced one long rainy season lasting from March/April to October. The mean monthly rain fall received the area was 109 mm in 2013 and 156 mm in 2014. The mean monthly minimum and maximum temperature was 19°C and 29°C in 2013, and 18°C and 27°C in 2014 according to South west Jima meteorological stations data. The soil of the area is characterized by sandy clay loam as determined by Jima Agricultural research Center soil and Water research processes soil laboratory.

Experimental treatments, design and procedures
Seven varieties were used for evaluation namely; Gudanie, Jallanie and Belete varieties obtained from Holeta Agricultural Research Center and Bule, Dancha, Marachare and Wochecha varieties obtained from Awassa Agricultural Research Center were used as a treatment. Treatments were arranged in randomized complete block design with three replications. Land was ploughed three times and all other management practices, such as seed and fertilizer rate, weeding, insect pest and disease control were applied as per the general recommendations for potato production [9]. The experimental field was divided in to three Blocks and each containing 7 plots with a distance of 1 m between block and 0.75 m between plots. Spacing between row 75 cm and between plants 30 cm was used. Planting was done in November 2013/2005 and 2014/2006.

Data collection and analysis
Data were collected on yield and yield components such as average tuber diameter, average tuber number, average tuber weight, marketable tuber number, unmarketable tuber number, total tuber number, marketable tuber yield, and unmarketable tuber yield and subjected to analysis of variance using GLM model in SAS software version 9.0 statistical packages. For factors showing significant difference, mean comparisons were made using LSD value at 5% significant level.

Results and Discussion
Analysis of variance (ANOVA) for yield and yield components were showed significant (p<0.05) difference among the varieties for all traits except average tuber diameter and marketable tuber number in 2013 (Table 1) and average tuber diameter and unmarketable tuber yield in 2014 ( Table 2). The presence of significant difference among the genotype for these traits was due to genetic variability of the varieties.  Based on the analysis highly significant (P<0.05) difference was observed among the varieties for average tuber number per hill at each year. Significantly highest average tuber number per hill was recorded by variety Marachare (18.8), while the least was recorded by Dancha (7.7), though Dancha and the second high yielded variety Bule were statistically not significant in 2013 (Table 3). The highest average tuber number per hill was also recorded by Marachare (21.41) followed by Gudanie, while the lowest was recorded by Wochech (8.4) ( Table 4).

Source of variation
The average tuber number per hill was higher in 2014 than 2013 possibly reflects the climatic factors more favourable in 2014 than 2013 during the tuber initiations stage.
The highest average tuber weight per hill was recorded by variety Belete (0.91 kg), while variety Gudanie (0.41 kg) produced the lowest average tuber weight in 2013 (Table 3). Variety Belete was produced significantly highest (1.4 kg) average tuber weight followed by Marachare, Gudanie and Blue, while Wochecha (0.49) was produced  (Table 4). Variety Belete was showed consistent average tuber weight in both seasons even though there was certain variations of rain fall in amount and distribution, and temperature in the area. In contrast, all varieties gave better average tuber weight in 2014 than 2013 indicating the season in 2014 was favourable for potato growth and development.
Varieties showed highly significant difference for marketable tuber number in 2014. However, this difference was not significant in 2013. Bule (337449) and Dancha exhibited the highest and the lowest marketable tuber number per hectare respectively in 2013 (Table 3). Marchare (696914) was given high and significant marketable tuber number, while Wochecha was given the lowest marketable tuber number in 2014 (Table 4).
Varieties were showed highly significant (P<0.05) difference for unmarketable tuber number per hectare in both season (Tables 1 and  2). Marachare (486831) had scored significantly highest unmarketable tuber number, while Dancha (61728) was recorded the lowest unmarketable tuber number though Dancha, Wochecha, Belete and Bule were statistically not significant in 2013 (Table 3). Variety Belete (53704) had the high unmarketable tuber number though it was statistically not significantly different from Dancha and Jallanie, while Marachare (8025) had lowest un marketable tuber number though Marachare and Gudanie were statistically not different in 2014 ( Table  4). The highest overall mean unmarketable tuber number was observed in 2013 (199941) than 2014 (30776) might be due to the shortage of rainfall during early stage and the presence of high rain fall around the harvesting time that result in tuber rote in turn increased unmarketable tuber number.
Varieties showed highly significant (P<0.05) difference for total tuber number in both years (Tables 1 and 3). The highest total tuber number was recorded by Marachare in 2013 (817284) and 2014 (704938). The lowest total tuber number was recorded by Dancha (312757) in 2013 through Danch, Wochecha and Belete were statistically not significant. On the other hand, Wochecha (171296) had scored the lowest total tuber number in 2014 though it was not significantly different from Danch and Jallanie. Although higher overall mean total tuber number exhibited in 2013, it was not as good as 2014, which had resulted in better overall mean marketable tuber number.
Among the varieties highly significant (P<0.05) difference was observed for marketable tuber yield in each year (Tables 1 and 2). Bletete (36.46 t/ha) had showed significantly highest marketable tuber yield in 2013; while the lowest marketable tuber number was obtained by Gudanie (13.53 t/ha), though Gudanie, Marachare, Jallanie and Dancha were not significant (Table 3). Belete had scored the highest (34.41 t/ha) marketable tuber yield though Belete, Gudanie and Marachare were statistically not different, whereas Wochecha (7.45 t/ha) had scored significantly lowest marketable tuber yield in 2014 growing season (Table 4). In contrast, highest overall mean marketable tuber yield was exhibited in 2014 (22.78 t/ha) than 2013 (21.88 t/ha) might be due to better climatic conditions in the former year. Varieties were showed marketable tuber yield variation over the years. This is in consistent with that of [11] who reported the significant influence of year × variety interaction on marketable tuber yield of potato.
The difference among varieties was highly significant for unmarketable tuber yield in 2013. However, this difference was not significant for unmarketable tuber yield in 2014 (Tables 1 and 2). Even though there was no significant difference among the varieties for unmarketable tuber yield high yield loss was observed in Marachare (6.63 t/ha) and low in Wocheacha (2.01t/ha) in 2014 (Table 4). In 2013 significantly highest yield loss was observed in Belete (5.5 t/ha), whereas the least yield loss was observed in Marachare (0.52 t/ha) ( Table 3). The significant difference among the varieties in 2013 indicates the varieties response differently to different extent of climatic variations. The very high and low prevalence of climatic factors such rain fall, temperature and humidity would affect the crop yield negatively. Similarly, Berga [12] reported that unmarketable tuber yield variation could be due to varietal differences. Moreover, it might be controlled more importantly by manipulating other factors such as disease incidence and harvesting practice, etc.
Among the varieties highly significant (P<0.05) difference were observed for total tuber yield in 2013 and 2014 (Tables 1 and 2). The highest total tuber yield was exhibited in variety Belete in 2013 (40.54 t/ha) and 2014 (39.98 t/ha). However, the lowest total tuber yield was displayed in variety Gudanie (18.23 t/ha) and Wochecha (10.1 t/ha) in 2013 and 2014 respectively. The highest overall mean total tuber yield was found in 2013 which was 25.97 t/ha, while 25.26 t/ha had got in 2014. As the overall mean indicates the total tuber yield was almost similar in both years even though some varieties showed yield difference across the years. Variety Belete was showed the highest and consistent tuber yield over years followed by Bule which was the second high yielded and consistent tuber yield ( Figure 1). The high yield variation was observed in 2014 than 2013 indicating the suitability of growing season to explore the genetic potential of the variety. In contrast, all varieties were scored far below than the national total tuber yield level [9] and the yield loss was ranged from 14.69% up to 51.02%. The reason might be due to the shortage of rain fall during the initial growth and development stage, occurrences of late blight disease and high rain fall occurrence around the physiological maturity that can enhance different disease like root rot. In general, Belete and Bule were showed consistence and better adaptability in the test area.

Summary and Conclusion
The analysis of variance for yield and yield components had showed highly significant (P<0.05) difference among the varieties for all studied traits except tuber diameter and marketable tuber number in 2013 and tuber diameter and unmarketable tuber yield in 2014. The presence of significant differences among the varieties indicates the genetic difference of varieties in yield potential, disease resistance and response to different climatic factors. The significance of traits in one year and not in another year indicates the extent of variation of response of traits to the existing variations in climatic factors in different year.
The result has revealed that there is no superior varieties for all tested characters in the analysis suggesting the traits are differently affected by genetic, agronomic and climatic factors. The mean performance of tested Varieties over testing years for total tuber yield was ranged from 40.257 t/ha for Belete in 2013 to 18.097 t/ha for Wochecha in 2014. All the varieties were scored far below than the national total tuber yield level and the yield loss was ranged from 14.69% to 51.02%. This might be due to the presence of high rain fall on ward to flowering stage and resulted in late blight and root rot disease, which obviously reduce the crop yield.
Although certain variations observed across the years in tuber yield for different varieties, Belet and Bule were showed high and consistent yield over years. Therefore, on the basis of present study Belete variety, which was given high yield in both years, could be used instated of currently using varieties to increase production and productivity of the potato crop in the area for better enhancement of food security and livelihood income. In the shortage of Belete, Bule could be used, which was second high yielded variety.
The research gap and future directions: agro ecological characteristics and soil fertility status of the area is being different from other area, planting date and fertilizer rate determination, seed degeneration study, new genotype introduction to release high yielding and disease resistant variety, pre extension and demonstration activity should be done.