Genetic diversity of Coffea arabica cultivars was estimated using amplified fragment length polymorphism (AFLP) markers. Sixty one Coffea accessions composed of six arabica cultivars, including Typica, Bourbon, Catimor, Catuai, Caturra and Mokka Hybrid, plus two diploid Coffea species, were analyzed with six EcoRI- MseI primer combinations. A total of 274 informative AFLP markers were generated and scored as binary data. These data were analyzed using cluster methods in the software package NTSYSpc. The differences among cultivars at the DNA level were small, with an average genetic similarity of 0.933. Most accessions within a cultivar formed a cluster, although deviant samples occurred in five of the six cultivars examined due to residual heterozygosity from ancestral materials. Among the six cultivars fingerprinted, the highest level of genetic diversity was found within the cultivar Catimor, with an average genetic similarity of 0.880. The lowest level was found within Caturra accessions, with an average genetic similarity of 0.993. Diversity between C. arabica and two other Coffea species, Coffea canephora and Coffea liberica, was also estimated with average genetic similarities of 0.540 and 0.413, respectively, suggesting that C. canephora is more closely related to C. arabica than is C. liberica. The genetic variation among arabica cultivars was similar to the variation within cultivars, and no cultivar-specific DNA marker was detected. Although arabica cultivars appear to have a narrow genetic base, our results show that sufficient polymorphism can be found among some arabica cultivars with a genetic similarity as low as 0.767 for genetic/QTL mapping and breeding. The assessment of genetic diversity among arabica cultivars provided the necessary information to estimate the potential for using marker-assisted breeding for coffee improvement.

We have used AFLPs to construct a genetic linkage map on a pseudo-F(2) population of arabica coffee ( Coffea arabica L.) derived from a cross between the cultivars Mokka hybrid and Catimor. Sixty trees from this population were selected on the basis of plant height distribution to construct a linkage map. A total of 456 dominant markers and eight co-dominant markers were generated from 288 AFLP primer combinations. Of the total number of markers generated, 68% were from cv. Catimor, 30% from cv. Mokka hybrid, and 2% were co-dominant. This distribution suggests that the heterozygosity within the cv. Catimor sub-genomes was twice that within the cv. Mokka hybrid sub-genomes. Linkage groups were constructed using MAPMAKER version 3.0, resulting in 16 major linkage groups containing 4-21 markers, and 15 small linkage groups consisting of 2-3 linked markers each. The total length of the map was 1,802.8 cM, with an average distance of 10.2 cM between adjacent markers. This genetic map will serve as the framework for mapping QTL controlling source-sink traits in the same population.

Because the duration of growth for commercial sugarcane (Saccharum spp. hybrids) production can vary from 9 to 36 mo, determining the optimum age at crop harvest is important to profitability. To account for variable climate across seasons and locations, there is a need to understand the physiology of yield accumulation and quantitatively describe the effects of crop age on productivity. Few field studies have been conducted to determine the factors responsible for yield variation in different cultivars of sugarcane at different crop ages, and the physiology of yield accumulation has rarely been examined on a dry matter basis with all yield components, including tops, millable stalk, trash, and roots. This paper compares above‐ and belowground biomass accumulation with crop age in two current cultivars grown in field experiments under drip irrigation in Hawaii from 1991 to 1993, and reanalyzes earlier experiments conducted in Hawaii in the 1930s and 1940s to examine historical changes in the pattern of yield accumulation in sugarcane. The key findings from this analysis are that (i) differences in yield accumulation during the first 12 mo of growth were not necessarily reflected in final yields at harvest at 18 to 24 mo; (ii) yield accumulation was less efficient in the second year of growth for current cultivars, but not necessarily so for older cultivars; (iii) belowground biomass decreased from 17% of total biomass at 6 mo to 11% of total biomass from 12 to 24 mo; (iv) there was no indication that older cultivars were less productive than current cultivars; and (v) yields rarely increased beyond 18 mo of age.

Intercepted radiation is a major driving variable of crop production under high‐input irrigated conditions. Quantitative information on the utilization of radiation in yield accumulation allows extrapolation beyond the current season and location, and when this information is incorporated into crop growth simulation models, the effect of crop age on the productivity of different cultivars can be examined under different climatic conditions. This paper examines the differential performance of high‐yielding sugarcane (Saccharum spp. hybrids) crops in terms of the amount of short‐wave solar radiation intercepted (Si) and the efficiency of use of intercepted radiation (RUE) in biomass production. Biomass accumulation during the 12‐ to 24‐mo crop cycle was examined for two experiments conducted in Hawaii, and three experiments conducted in tropical Australia from 1991 to 1993. The analysis showed that (i) RUE was much less for growth after 12 mo than in the first 12 mo; (ii) maximum RUE of sugarcane approaches 2.0 g MJ−1; (iii) biomass accumulation beyond 12 mo was not related directly to radiation utilization; and (iv) cultivars differed in S19 but differences in RUE could not be unequivocally assessed due to the confounding effect of variable recovery of trash in biomass estimates. It is concluded that stalk death and consequent biomass loss are important factors contributing to yield variation in sugarcane crops growing for 12 to 24 mo, with a yield plateau occurring at variable crop ages during the second year of growth.

Hawaiian sugarcane cultivars(SaccharumL. hybrids) differed considerably in their tolerance to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). There was a greater concentration of diuron in the younger leaves of a sensitive cultivar, ‘H 53–263,’ compared with a tolerant cultivar, ‘H 50–7209′; degradation of diuron was more extensive in ‘H 50–7209′. The metabolites identified after applications of carbonyl-labeled diuron to the root system were 1-(3,4-dichlorophenyl)-3-methylurea (monomethyl-diuron) and 1-(3,4-dichlorophenyl)urea (demethylated diuron). Differences in diuron phytotoxicity to cultivars ‘H 53–263’ and ‘H 50–7209’ are at least partially explained by differences in the distribution and degradation of diuron.