Darwin and the White Shipwrecked Sailor: Beyond Blending Inheritance and the Jenkin Myth.

This paper revisits Fleeming Jenkin's anonymous review of Charles Darwin's Origin of Species, published in the North British Review in June 1867. This review is usually revered for its impact on Darwin's theory of descent with modification. Its classical interpretation states that Jenkin, a Professor of Engineering at the University of Edinburgh, made a compelling case against natural selection based on the fact of "blending inheritance" and the "swamping" of advantageous variations. Those themes, however, are strikingly absent from Jenkin's text. They were later read into Jenkin's text by scholars trying to explain how Darwinian selection was reconciled with Mendelian genes and the birth of the Modern Synthesis. While many scholars have tried to measure Jenkin's effect on Darwin, the value of the 1867 review remains unclear. This paper re-examines its content and concludes that Jenkin's "able review" was in fact written by an engineer whose competencies in biology were very low. Focusing on the figure of the shipwrecked white sailor isolated on an island inhabited by Black people, this paper also underlines the racial assumptions behind Jenkin's review. "Blending inheritance" is thus a theme linked to theoretical reworkings on the question of race and skin colors, taking its root in Galton's typology of heredity. Darwin was probably mostly unimpressed by Jenkin's review. The problems raised by the review were not so much "blending inheritance" and "swamping" but a conundrum of problems related to the effects of intercrossing on variation and reversion.

Molecular and Morphological Characterization of Introgression Lines with Resistance to Bacterial Leaf Blight and Blast in Rice.

The present study evaluates marker assisted forward breeding (MAFB)-derived disease resistant introgression lines (ILs) which do not have the targeted resistance genes for bacterial blight (xa5 + xa13 + Xa21) and blast (Pi2 + Pi9 + Pi54). The ILs were derived in the background of two elite rice cultivars, Krishna Hamsa [Recurrent Parent 1 (RP1)] and WGL 14 (RP2), involving multi-parent inter-crossing. Molecular characterization with gene specific markers for seven reported resistance genes each for bacterial blight (Xa33, Xa38, xa23, Xa4, xa8, Xa27 and Xa41) and blast (Pi1, Pi20, Pi38, Pib, Pitp, Pizt and Pi40) revealed the presence of xa8 and Xa38, in addition to the targeted xa5, xa13 and Xa21 for bacterial blight resistance and Pi1, Pi38, Pi40, Pi20, Pib and Pipt, in addition to the targeted Pi9 and Pi54, for blast resistance in various combinations. A maximum of nine resistance genes xa5 + Xa21 + Pi54 + xa8 + Pipt + Pi38 + Pi1 + Pi20 + Pib was observed in RP1-IL 19030 followed by eight genes xa5 + xa13 + Xa21 + xa8 + Pi9 + Pipt + Pi1 + Pi20 in two RP2-ILs, 19344 and 19347. ANOVA revealed the presence of significant variability for all the yield traits except "days to 50% flowering" (DFF). Box plots depicted the seasonal differences in the phenotypic expression of the yield traits. There was significant positive association of grain yield with days to flowering, tiller number and panicle number. Thousand grain weight is also significantly and positively correlated with grain yield. On the contrary, grain yield showed a significantly negative association with plant height. Multi-parent selective inter-crossing in the present study not only led to the development of high yielding disease resistant ILs but also enhanced recovery of the recurrent parent via selection for essential morphological features. More than 90.0% genetic similarity in the ILs based on SNP-based background selection demonstrated the success of multi-parent selective intercrossing in the development of disease resistant NILs.

New insights into trait introgression with the look-ahead intercrossing strategy.

Trait introgression (TI) can be a time-consuming and costly task that typically requires multiple generations of backcrossing (BC). Usually, the aim is to introduce one or more alleles (e.g. QTLs) from a single donor into an elite recipient, both of which are fully inbred. This article studies the potential advantages of incorporating intercrossing (IC) into TI programs when compared with relying solely on the traditional BC framework. We simulate a TI breeding pipeline using 3 previously proposed selection strategies for the traditional BC scheme and 3 modified strategies that allow IC. Our proposed look-ahead intercrossing method (LAS-IC) combines look-ahead Monte Carlo simulations, intercrossing, and additional selection criteria to improve computational efficiency. We compared the efficiency of the 6 strategies across 5 levels of resource availability considering the generation when the major QTLs have been successfully introduced into the recipient and a desired background recovery rate reached. Simulations demonstrate that the inclusion of intercrossing in a TI program can substantially increase efficiency and the probability of success. The proposed LAS-IC provides the highest probability of success across the different scenarios using fewer resources compared with BC-only strategies.

Multiparent-Derived, Marker-Assisted Introgression Lines of the Elite Indian Rice Cultivar, 'Krishna Hamsa' Show Resistance against Bacterial Blight and Blast and Tolerance to Drought.

Major biotic stresses viz., bacterial blight (BB) and blast and brown plant hopper (BPH) coupled with abiotic stresses like drought stress, significantly affect rice yields. To address this, marker-assisted intercross (IC) breeding involving multiple donors was used to combine three BB resistance genes-xa5, xa13 and Xa21, two blast resistance genes-Pi9 and Pi54, two BPH resistance genes-Bph20 and Bph21, and four drought tolerant quantitative trait loci (QTL)-qDTY1.1, qDTY2.1, qDTY3.1 and qDTY12.1-in the genetic background of the elite Indian rice cultivar 'Krishna Hamsa'. Three cycles of selective intercrossing followed by selfing coupled with foreground selection and phenotyping for the target traits resulted in the development of 196 introgression lines (ILs) with a myriad of gene/QTL combinations. Based on the phenotypic reaction, the ILs were classified into seven phenotypic classes of resistance/tolerance to the following: (1) BB, blast and drought-5 ILs; (2) BB and blast-10 ILs; (3) BB and drought-9 ILs; (4) blast and drought-42 ILs; (5) BB-3 ILs; (6) blast-84 ILs; and (7) drought-43 ILs; none of the ILs were resistant to BPH. Positive phenotypic response (resistance) was observed to both BB and blast in 2 ILs, BB in 9 ILs and blast in 64 ILs despite the absence of corresponding R genes. Inheritance of resistance to BB and/or blast in such ILs could be due to the unknown genes from other parents used in the breeding scheme. Negative phenotypic response (susceptibility) was observed in 67 ILs possessing BB-R genes, 9 ILs with blast-R genes and 9 ILs harboring QTLs for drought tolerance. Complex genic interactions and recombination events due to the involvement of multiple donors explain susceptibility in some of the marker positive ILs. The present investigation successfully demonstrates the possibility of rapid development of multiple stress-tolerant/resistant ILs in the elite cultivar background involving multiple donors through selective intercrossing and stringent phenotyping. The 196 ILs in seven phenotypic classes with myriad of gene/QTL combinations will serve as a useful genetic resource in combining multiple biotic and abiotic stress resistance in future breeding programs.