Weed ecology and economic importance of Emilia javanica (Burm.) Rob. and E. sonchifolia (L.) DC
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1975
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Abstract
The Emilia species and types in Hawaii were studied with respect to their taxonomy and life history, importance as disease reservoirs for the tomato spotted wilt virus, and as a weed competitor with crop plants like lettuce (Lactuca sativa L.), mustard cabbage (Brassica juncea Czern. & Coss.), sweet corn (Zea mays L.) and transplanted tomato (Lycopersicon escu1entum L.). Of the four Emilia species reported in Hawaii, only E. javanica (Burm.) Rob. and E. sonchifolia (L.) DC were found on the islands of Oahu and Kauai, while on Lanai only the Red and Orange types of E. javanica were observed. The E. javanica type Purple was found only in limited areas on Oahu and Kauai. The E. javanica types, particularly the Red type, which were referred to as E. sonchifo1ia or E. sagittata (Vahl) DC by other workers, are the most predominant types on Oahu, Kauai and Lanai. The similarities in vegetative and floral morphology of the different color types of E. javanica, in addition to their ability to interbreed indicate that they belong to the same species. Plant height, capitulum size, number of achenes (seeds) per capitulum, number of capitula per plant were influenced by fertilizer and shading •treatments. The E. javanica types were taller (50 to 62 cm) than E. sonchifolia (19 to 30 cm) at flowering. Fertilized Emilias under 55% shade were tallest while unfertilized plants under full sunlight were shortest. The total length of the capitulum of the E. javanica types ranged from 12.5 to 13 mm compared to E. sonchifolia with 10.5 to 11 rom. When fertilized with N-P-K and grown in full sun-light, the Orange, Red and Purple types of E. javanica had 70, 64 and 57 seeds per capitulum, respectively, while E. sonchifolia had 60. Among the Emilias, the E. javanica type Purple produced the greatest number of capitula per plant. The earliest to mature (seed to seed) was the Purple type of E. javanica (48 ± 2 days), followed by the Red (51 + 1 days), Orange (52 + 1 days), and E. sonchifolia (53 + 3 days) was the latest. Seed germination studies showed that seeds of E. javanica matured earlier than E. sonchifolia. However, viable seeds were formed in both species before the capitula were ready to dehisce. All Emilias examined produced both light and dark colored seeds. The seeds of the Emilia species and types required light for germination up to a period of 4 weeks after harvest. Germination and dormancy varied with seed color, species, and types. Newly harvested seeds of E. sonchifolia germinated better under a wider temperature regime (15 to 35 C) than the E. javanica types (25 to 35 C). Flowering response of the Emilia species and types were day neutral with respect to photoperiod. Observed differences in the time of flowering were due to differential rates of inflorescence development than to differential initiation of the floral primordium. Plants grew taller as the photoperiod was lengthened. Transmission studies by sap inoculation of the tomato spotted wilt virus (TSWV) showed that all the types of ~. javanica (Orange, Red and Purple) and ~. sonchifolia harbored and transmitted the TSWV to tomato 'Tropic' and lettuce 'Anuenue'. The two species of Emilia differed with respect to infection with TSWV. E. sonchifolia gave a lethal reaction while the E. javanica types tolerated infection of the virus. The TSWV from tomato and lettuce were re-transmitted back to the Emilias. Pure stands of E. javanica type Red grown at specific densities with lettuce 'Anuenue', mustard cabbage 'Waianae', sweet corn 'H-68', and transplanted tomato 'N-52' demonstrated that the effects of Emilia on crop growth and yield varied with crop species. For example, full season competition of Emilia at 11 weeds per crop plant decreased the dry weights of lettuce and mustard cabbage by 70 to 30%, respectively. Sweet corn fodder was not affected even with 150 weeds per crop plant, while transplanted tomato fruit yield was reduced 18% by 80 to 126 weeds per crop plant. Because non-limiting irrigation was supplied, differences in response to Emilia competition depended on the crop plant's ability to compete for light and nutrients.
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Typescript.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1975.
Bibliography: leaves 129-138.
xii, 138 leaves ill. (some col.)
Thesis (Ph. D.)--University of Hawaii at Manoa, 1975.
Bibliography: leaves 129-138.
xii, 138 leaves ill. (some col.)
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Weeds -- Hawaii
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Agronomy and Soil Science; no. 806
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