Agronomic Performance of New JKUAT Papaya (Carica Papaya L.) Hybrids in Different Agro-Ecological Zones of Kenya

Abstract

There has been low papaya production in Kenya due to poor and low quality seeds that results to low yield accompanied by poor quality. The seeds majorly utilized for propagation are selected by farmers from their previous production and seed that are imported. However, this is not satisfactory since the imported seeds are costly and very few farmers can afford. In addition, most of the selected seeds by farmer have poor adaptability and get infected mostly by papaya viral diseases. The challenges mentioned above showed a gap that therefore necessitated the development of new JKUAT papaya lines. These newly developed lines have been evaluated institutionally and have shown good qualities that can help boost papaya production. This study therefore evaluated the performance of newly developed JKUAT papaya lines (Line 1, Line 5, Line 6 and Line 7) in selected agro-ecological zones of Kenya. The seedlings were raised at JKUAT and latter transplanted after three months to four different study sites; KARLO Mwea and JKUAT(Upper Midlands zones), Nkubu and Mitunguu(Upper Highlands zones). The papaya lines were planted in a randomized complete block design with three replications. Data were collected on their morphological and fruiting characteristics, namely trunk, height, internode length, time to flowering, total number of fruits, flesh thickness, fruit diameter, fruit length, fruit weight and quality parameters. From the result, line 5 in Mwea had the highest number of fruit, followed by line 6 in Mitunguu and then line 5 in Nkubu, while on the other hand, line 1, 7 and solo had the least number of fruits. Fruits from lines 5 and 6 had small to medium size, while those of lines 1, 7 and solo were large in size. Fruit weight was significantly different where the highest was recorded by line 7 in Mitunguu( 2kg), followed by line 1 in Mwea(1.85 kg) while the least was recorded by line 5 in JKUAT (1.19 kg) followed by line 5 in Mitunguu (1.35 kg). The papaya lines had a significant differences on flesh thickness where the highest was recorded by line 7 at JKUAT (1.81cm), followed by line 7 at Mitunguu, Nkubu and Mwea (1.80 cm), however on the other hand, the least was recorded by line 5 at JKUAT (1.56 cm), line 5 at Mwea (1.60 cm) and line 5 at Mitunguu (1.60 cm).The results also showed significant differences in height at the first flower emergence. Sunrise solo had the first flower at 92.33 cm at KALRO Mwea while the shortest height at first flower emergence was in Line 6 (69.97 cm) at JKUAT. The total soluble solids (TSS) varied significantly from 14 % in line 5 in Mitunguu to 8.33% in line 7 at Mwea. From the study conducted, all the sites experienced incidences of powdery mildew except JKUAT and among the locations with incidences, there were no significant differences that were noted on both incidences and severity levels. However, there were significant differences that were noted in papaya lines where line 1 at KALRO Mwea had higher incidences and severity (2.4% and 1.25% respectively). The incidence of anthracnose disease was observed at JKUAT only with 2.53% and a severity of 3.34%, while other experimental sites did not show any symptom. Among the lines, lines 6 and 7 did not show symptoms while line 1, 5 and solo sunrise had incidences but they did not have significant differences. The interactions between the locations and papaya lines among the lines with symptoms did not show significant differences, however solo at JKUAT had a higher incidence of 4.58% while line 1 at JKUAT had a higher severity of 6.97%. Incidence of papaya ringspot virus was noted in all the experimental locations and they showed significant differences with JKUAT having a higher incidence and severity of 6.84% and 10.04% respectively, while on the other hand, Nkubu had the least incidences and severity of 2.05% and 1.92% respectively. Among the papaya lines, line 5 had higher incidences while solo had the lowest levels of 5.98% and 2.67% respectively. There were also significant differences noted on the severity of ringspot virus where line 7 had higher severity levels of 7.92% while the least severity was recorded by solo at 2.84%. In conclusion, different JKUAT papay lines exhibited different agronomic performances both in growth, development and disease resistance where by for the combined traits, line 7 performed highest in fruit weight, fruit diameter and flesh thickness while line 5 was better in total number of fruits and total soluble solids. In addition, lines 5, 6 and 7 were not susceptible to fungal infections in different sites i.e. line 5 free from powdery mildew at KALRO Mwea and Nkubu, line 6 free from powdery mildew at Nkubu and Mitunguu and also free from anthracnose at JKUAT. The study recommends further research to evaluate the performance under other conditions such as heat and water stress .