Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is a chief factor limiting rice productivity worldwide. XM14, a rice mutant line resistant to Xoo, has been obtained by treating IR24, which is susceptible to six Philippine Xoo races and six Japanese Xoo races, with N-methyl-N-nitrosourea. XM14 showed resistance to six Japanese Xoo races. The F2 population from XM14 × IR24 clearly showed 1 resistant : 3 susceptible segregation, suggesting control of resistance by a recessive gene. The approximate chromosomal location of the resistance gene was determined using 10 plants with shortest lesion length in the F2 population from XM14 × Koshihikari, which is susceptible to Japanese Xoo races. DNA marker-assisted analysis revealed that the gene was located on chromosome 3. IAS16 line carries IR24 genetic background with a Japonica cultivar Asominori segment of chromosome 3, on which the resistance gene locus was thought to be located. The F2 population from IAS16 × XM14 showed a discrete distribution. Linkage analysis indicated that the gene is located around the centromeric region. The resistance gene in XM14 was a new gene, named XA42. This gene is expected to be useful for resistance breeding programs and for genetic analysis of Xoo resistance.

To improve understanding of the dynamics of the cassava mosaic disease (CMD) pandemic front, geospatial approaches were applied to the analysis of 3 years' data obtained from a 2-by-2°(approximately 222-by-222 km) area of northwestern Tanzania. In total, 80 farmers' fields were assessed in each of 2009, 2010, and 2011, with 20 evenly distributed fields per 1-by-1°q uadrant. CMD-associated variables (CMD incidence, CMD severity, vector-borne CMD infection, and vector abundance) increased in magnitude from 2009 to 2010 but showed little change from 2010 to 2011. Increases occurred primarily in the two westernmost quadrants of the study area. A pandemic "front" was defined by determining the values of CMD incidence and whitefly abundance where predicted disease gradients were greatest. The pandemic-associated virus (East African cassava mosaic virus-Uganda) and vector genotype (Bemisia tabaci sub-Saharan Africa 1-subgroup 1) were both present within the area bounded by the CMD incidence front but both also occurred ahead of the front. The average speed and direction of movement of the CMD incidence front (22.9 km/year; southeast) and whitefly abundance front (46.6 km/year; southeast) were calculated, and production losses due to CMD were estimated to range from US$4.3 million to 12.2 million.Cassava mosaic disease (CMD) is one of the most important constraints to cassava production in sub-Saharan Africa, and causes more than US$1 billion of losses annually (Legg et al. 2006;Thresh et al. 1997). The disease is caused by several species of cassava mosaic begomoviruses (CMB) (family Geminiviridae, genus Begomovirus) (Bock and Woods 1983), which are propagated through planting infected stem cuttings and transmitted persistently by the whitefly Bemisia tabaci (Genn.) (Dubern 1994). In the late 1980s and early 1990s, an epidemic of unusually severe CMD emerged in Uganda ) and subsequently spread to affect a large area of East and Central Africa (Legg 1999;Legg et al. 2006;Otim-Nape et al. 1997). A novel virus recombinant, East African cassava mosaic virus-Uganda (EACMV-UG) was shown to be associated with this "pandemic" (Zhou et al. 1997) and gave rise to unusually severe disease symptoms through a synergistic interaction with a second CMB, African cassava mosaic virus (ACMV). Severe CMD spread rapidly at estimated speeds of 20 to 30 km/year (Otim-Nape et al. 1997), driven by superabundant populations of B. tabaci (Legg and Ogwal 1998). Almost 30 years after the first reports of severe CMD from Uganda, the severe CMD pandemic continues to spread, currently advancing southward through eastern Democratic Republic of Congo and westward through central Cameroon. The pandemic of severe CMD continues to pose a threat to the world's largest producer of cassava, Nigeria, lying immediately to the west of Cameroon.Monitoring and surveillance activities have played a vital role in the CMD management effort as newly affected areas have been identified, facilitating the targeting of control interventions. An important aspect...

Improvement of resistance against rice bacterial blight (BB) disease is an important breeding strategy in breeding programs across the world, especially in Africa and southern Asia where BB is more prevalent. This report describes a high-resolution map and characterization of xa42 at XA42 locus, a rice BB resistance gene in XM14, a mutant line originating from IR24. The candidate gene region was narrowed down from 582 kb, which had been obtained in our previous study, to 57 kb. XM14 shows brown spots in its leaves like lesion mimic mutants. This line also shows a shorter stature than the original cultivar IR24. In XA42 gene segregating populations, homozygotes of xa42 allele were consistently resistant to the six Japanese Xanthomonas oryzae pv. oryzae races used for this study. They also showed brown spots and markedly short stature compared with the other genotypes, suggesting that xa42 gene exhibits pleiotropic effects.